Oh, nice, that's a great tip!
Regarding the mega XP thing, basically every earning of XP is a thousand. Shooting sticky spores, weakspot kills, silent, whatever. It actually can be a few thousand per kill this way. I don't know how much each operator needs, but it's several million and should take a few missions, each.
And regarding the timer lock, the game seems to still match a delta between the time the round started and when you disable the option, so you might find yourself running to zero immediately upon disabling the timer. Just a forewarning. The timer freeze option will also cause you to shake a bunch and fail to interact with stuff, so toggle it off if you have issues with objectives or simply leaving the mission/area.
To add onto the mega XP option.
There seems to be a cap on XP gain, in the sense that I've tried "farming" XP as much as possible, and it'll still only land me on level 5 or 6.
Then by doing the exact same again, it'd cap be at level 8 for the next run.
Then finally the 3rd run brings me up to level 10.
By using the mega XP option, while it not only helps level operators faster, but by doing so, it also indirectly helps level up the Tech progression easily. There's enough tech points for all the unlocks, so really just level all your characters a bunch, and you'd reach Tech tier 5 in no time. **This part of comment is more in regards to somebody saying the Tech points option doesn't work.