The Time Offset (actual GPS Time -18s= UTC) come within the GPS signal. Please find the way to read out this from the GPS signal and use it for showing the real UTC and show it in GPS Info for using together with other software like Smart Time sync which also ignoring the offset. At time i have to read first the actual number of Leap seconds and then i have to type it manually in the time sync software. I do not use automatic time scnc because the network time is sometimes wrong. And i have to set the time manually because i don't use a system with root access. But with Smart time sync works it nice. If GPS Time -18s is at xx:50 then 10 9 8 7 6 5 4 3 2 1 0 and set time..... I know this is also a issue for the time sync software but it will be not bad for mapfactor navigator.
Why do you assume, that GPS time is more accurate than the time coming from an NTP server (I assume NTP time will be the time of your network provider)? Anyway there is no relation to the problem recently coming up from the time problems arising out of weak electricity networks. https://www.heise.de/newsticker/meldung/Zeit-Synchronisation-per-Stromnetz-Energieknappheit-laesst-Uhren-nachgehen-3984126.html And if Android will not allow to set the time automatically without root for SmartTime, it will not allow to do Mapfactor Navigater this job either.
"Why is this so important? Do you have a specific need?" I don't use the mobile internet and have always when i going outdoor no internet. The gps signal is everywhere and send everytime the accurate time to the earth, but the android smartphone use the network time of the gsm provider. But my mobile phone provider have sometimes a wrong network time. (a half minute wrong). The best time coming from the gps satellites, thats true. Sure, the NTP is a good time source, ca GPS time + 0,8s. But the internet is not everywhere like the gps signal.
The location object (from the location api) returns the UTC time (getTime()) in milliseconds (since January 1 1970).
I assume MNF uses (can use) this as it is part of the "bulk data" (like latitude, longitude, altitude, bearing, etc), retrieved via the location object.
"I am not sure if I understand fully what Matthias wants" - The GPS Clocks run and run and run, and never will be there a Leap second in this time. But The UTC have Leap Seconds. But the GPS Satellites send this Leap second offset (since 01/ 2017 18s) within the signal. It should be possible to find this in the "location api".
I bought now the Samsung Galaxy XCover 4 (SM-G390F) with Android 7.0. And here works it. GPS Time use here the Offset. I am happy about. This is jst a Android Problem. The GPS in the olderSamsung Galaxy Xcover 3 (SM-G388FDSADBT) (Android 5) works not precise enough. Therefore bought i the new one because the small Galaxy Y made without glonass better gps tracks, i not yet testet how precise the GPS of new Smartphone works, but i guess better because it use also the chinese gps and notebookcheck.com made good test results.