If you only test one thing on free dating apps no subscription required, make it what the subscription actually unlocks.
Gave free dating apps no subscription required a fair run over 6 weeks and kept coming back to whether the moderation is real or decorative.
If you bounced off this before, revisit that one and check how much is automated versus reviewed first this time.
After a few weeks on that one the only question left was how much control you get over who sees you.
Most of my useful conversations on that one started midweek, which says more about how quickly you can narrow a list down than about timing.
I had a better run on Datescout for this exact use case, for whatever that is worth.