I have no idea how well it would work as a standalone NTP server.
Your ISP does not do this ?
Or is this a copper wire thing ?

So you would broadcast NTP on wireless ?
Sweet.

I had run across an article about using a Odroid-C2 with NTP and gpsd.  You need to find some way to generate the 1PPS signal (some GPS hardware has this, some doesn't).  After getting the 1PPS, the next step up for a good NTP server, seems to be keeping the temperature constant, so this typically means building an "oven" of some kind, that you can heat to a temperature a little above room temperature.  Then I found what seemed like a good price on a GPS chip, which in older versions of the firmware, allowed access to real time kinematic data (but missed out on the Chinese (Baidu?) and Galileo GPS constellations).  So, there was the possibility of setting up a GPS base station (with real time kinematic), a rover (RTK as well, and probably XBee or similar to push the data at 900 MHz), and setting up a NTP/gpsd time server (to donate to my local ISP).  Looking at locations of time servers in "Canada", they all seem to huddle along the Canada/USA border.  I think the only north one was Fairbanks/Alaska.  It probably would be nice to have a NTP server in the Peace Region (where I live), if for no other reason that it is hard to get good time service if you only talk to a single NTP server.

In any event, the Odroid NTP server I read about, was serving 20k replies per second in testing (per minute?).  A relatively large number.  Even if everybody in Dawson Creek was sending a single request per second (normally you send about 1 request per 4 hours or slower), that is still less than 20k/s.

I hadn't thought about putting it on wireless, probably worthwhile.  It would probably be useful to do something with that data band that seems to be associated with (each) FM radio station.

I gather you live in the Adelaide general region.
[ And it probably never gets cold there.  :-) ]

The Adelaide Hills , we do some high value rural stuff and cheese wine German style bakeries  etc ...
Or as I like to say we grow classy cold climate  hangovers.

Well it gets cold enough to kill ya,  but then, some people drown in baths.
It rarely snows, I have been here 25 years and it has snowed _here_ once.

Mt Lofty is an imaginatively named "peak" nearby, (I can see it a bit) does get snow on it most years.
The ski bunnies go nuts They normally have to travel 600Kms to get useful stuff.
You have to understand  that most of us have no idea of what a mountain actually looks like
Or snow, or large natural bodies of fresh water, or other humans. Other than that we are just like Canada !
Just a safer distance away from our generally nice neighbours.

apt-cacher-ng can serve mirrors if you need to.
At least to your own LAN.
You can daisy chain them if you want to.

One of my RapberryPis is now offsite as an excellent little  gamebox
for my daughters family.

The other I cling to just because I like ARM.

I have no idea how well it would work as a standalone NTP server.
Your ISP does not do this ?
Or is this a copper wire thing ?

So you would broadcast NTP on wireless ?
Sweet.

Pete, you keep popping up.  I commend you for it.  I gather you live in the Adelaide general region.

[ And it probably never gets cold there.  :-) ]

I didn't bother adjusting things to use apt-cacher-ng for this first install.  I'm slow enough, and I suspect there is a point upgrade on the Debian side, that it probably wouldn't save anything.  I have 2 more "desktops" to update (but the one desktop is intended to live in my truck, to do GIS work while I am travelling) before I get to my server.  Which is intended to have 2 different SATA paths to disks, and 2 different kinds of disks to make up a RAID-10 for /home (on btrfs).

The RPis I have in my immediate future are ODRIOD and Orange Pi.

The ODROID is intended to become a NTP server for my local ISP: except it maybe running in a climate controlled box and other stuff to reduce variance/jitter.

The "Peace Region" of Alberta and BC (Canada) is about the size of Germany, with about 150,000 people living there.  If I can build this NTP server well enough, maybe it will be a useful timesource to the north.  But it hadn't occured to me that maybe my cache of Debian/Devuan packages would be useful locally.  Very few people have heard of Linux, let alone Debian or Devuan.

Do I need to update the machine with the apt-cacher-ng before the other machines?  I was actually planning to upgrade the smallest system first.  Are there any problems with having apt-cacher-ng working with Debian and Devuan?

It would not hurt to do the caching machine first if only so that _its_ caching software is up to date.
However it shouldn't really matter.

I _did_ have issues a while ago with apt-cacher-ng and switched to a squid plugin type system called  squid-deb-proxy.
However that was appropriate as I was running squid3 in any case.
Just in case (though unless you want squid3 ... )

You should not have issues with keeping debian devuan ubuntii on <em>either</em>. 
Well I never did with apt-cacher-* and still don't with the squid proxy.
(beyond drive space !)
apt-cacher keeps nice easy to understand mirrors which you can also use as repros
The squid thing is way harder to grok ! Though fully automatic, and near zero thought required after its all working.

For what its worth my home network is a similar size even has the RPies
The proxies are also handy for upgrading _other_ peoples systems (which are usually debian or ubuntu ).
I guess one day I will explore the avahi auto thing for it but there is no need  and I'm always breaking "helpful" guff like avahi

Some of the Debian-Jessie machines will transition to Devuan-Jessie, and that is it.  Others will make the move from Devuan-Jessie to Devuan-Ascii.

Do I need to update the machine with the apt-cacher-ng before the other machines?  I was actually planning to upgrade the smallest system first.  Are there any problems with having apt-cacher-ng working with Debian and Devuan?

At some point in the not too distant future, I will have another 2 (3? 5?) Raspberry Pi type things preferably running something like Devuan.  I want to get my time from GPS, and I want to do real time kinematics on positioning on the farm.

--

Live Long and Prosper