You can also use JOSM to convert .ubx to .gpx. Simply change the filename extension to .nmea, open the file, and save it as .gpx. If the file contains lines which are not NMEA messages, JOSM will notify you and discard those lines. (.ubx files do usually contain non-NMEA messages.) JOSM will colour-code the trace according to the type of fix: RTK, float RTK, DGPS, etc. It preserves the colours in the converted .gpx file. As Stephane said, JOSM allows you to set offsets between GPS time and camera time which are not whole numbers of seconds. JOSM also correctly converts subsecond timestamps when converting from NMEA to gpx. Not all conversion software does this.

I managed to get the ‘attic’ (historical) data for Northwick Park Hospital at annual intervals from 2012 to 2021. There are hardly any buildings except in 2021. So any buildings that may have been there, were there for less than a year.

It wasn’t easy to get the data. I spent some time tweaking the Overpass query before I found a query that didn’t time out. It didn’t seem reasonable to try to fix the problem by extending the time-out from the default of three minutes.

I tried the method described by tyr_asd. It was easier to get the data, but I had trouble with QGIS. It just showed a blank, white map, although the objects were there. I had to quit and relaunch QGIS to get it to work properly. The use of the temporal slider was very effective. It showed there were hardly any buildings from 2012 (the start time I chose) until late 2020.

The u-blox NEO-7P does precise point positioning. I wrote about it briefly on talk-fr https://lists.openstreetmap.org/pipermail/talk-fr/2016-March/080463.html I am impressed with it, provided that you have a good view of the sky; and provided that, after startup, you wait for ten minutes for it to reach the best accuracy, before recording tracks.