at a rough guess I'd say that for every 90 minute test flight, I probably do 2-3 days of preparation, and at-least half a day of reporting and analysis.
Yup, I'd agree with that. BPF has accurately captured the main theme - tedious. In one case, I was required to make 64 three minute timed climbs in a DA-42, to gather climb performance data. Much more than three days analyzing that! Happily, most of the test flying I do is validating handling, rather than performance, so less post flight analysis.
But the only "glamour" associated with it, is that you walk out to the "new" or "different" plane on the ramp. Otherwise, it's hours of tedium, with moments of "Oh boy, here we go....
If you are in the right place, at the right time, with nearly enough experience, test flying will call you. Knocking at the TP door will be time consuming, focus on just being where the work is being done, and learning from those doing it now. When they step back, you could be next in line - I was....