The date is different on the builds, Firefox Nightly comes straight from mozilla central, whenever a new changed is introduced, updates twice per day -- the next version number jump doesn't happen until 61 reaches Beta, once 60 reaches stable on May 9th.

The name nightly gives a hint, that it updates every night. It is a development build. If you aren't comfortable running nightly, I suggest installing Firefox release, which is the build we recommend most people run.

Nightly updates twice a day or more when a respin is necessary, so you can get a lot updates with this version. Beta and Developer Edition update twice a week, so that is still a lot more then the current release.

Any specific reasons you are using Nightly and not a release or possibly a beta version?

See also:

• https://www.mozilla.org/en-US/firefox/channel/desktop/

If you notice the 20180424220100 as that is the build date time. Apr 24, 2018 and time.

You can click on the about:buildconfig that is on the about:support page for the source it was built from. All of the about urls for the build are listed in about:about

The Nightly channel as said gets checkins with two updates each day as a result with maybe the occasional respin build. While this may be a way to see new changes and features in the works early it can also lead to issues until it is fixed, finished or reverted.

The Firefox useragents for every channel build used to also be a way to show the exact build you have with the build date however this was stopped as of Firefox 16.0.2 and on in order to reduce the unique fingerprinting. The useragents have been more generic since then.