based on your response, my guess is you are not looking for a super tamper proof solution, also it can’t be a solution that requires costly network server updates, and your users are not the kind who will start using decompilers to try and change the ionic app - they will most likely only try system time changes and any other “simple” user hacks they might discover along the way as they go along. Is that right?
If so, you might want to use a combination of what @anna_liebt suggested and the monotonic clock (elapsed boot time).
A) If you are saying the advanced-geolocation-plugin returns network time and you have validated it does this without an active network connection, thats great. You should use it for devices where it works (note that iOS does not seem to be supported)
B) In addition to that, you can get the monotonic timer to measure time since boot and store the latest value and system time for each log. Lets assume the first log will be correct - there are many ways to enforce that, including one time network registration while installing the app. That way you can compute if they suddenly go “very different” (I wouldn’t complain if its a small drift) which might mean the user changed time, or the phone rebooted. If its the latter, and you detect this huge change happening very often, it should raise a flag - why would a user reboot so often and every few days?
You can easily use any cordova plugin in Ionic even if its not part of native. Google around. Start here
Between A + B you have a solution that should deter casual manipulation. An ideal phone will support both mechanisms. For some phone, you may need to fallback to one or the other. Note that it is always useful to check Android’s adoption before you worry about how many devices will fail - you can see current distribution here -obviously this data can be skewed against your situation - that you would know better than me
The only caveat here is I haven’t used either plugin myself - so if you discover they have issues, well, then, you’ll have to look for other solutions.