Also, your hashrate is too low (a single card) for reliable results after 24h because you're too dependent on luck. A single card won't get that many shares in and they all have different luck. The average pay for a 24h will vary quite a bit.
Hmm... I'll give Flypool a shot, but I'm afraid I can't do anything about only dedicated 1 GTX 1080 to each miner for these tests right now - or for the immediate future - as GPUs simply aren't available unless you want to pay fuck-you prices.
I have to concede your point about pool luck, though. Luckpool was finding a block every few minute, but that information seems to be out-of-date because I just checked the blocks tab and it looks like the average TTF is now 1.1 hours, so 24 hours with a single card is, indeed, way too short of a time period.
BUT... if the TTF is less than 5 minutes then a 24 hour test based on payout should be just as accurate as counting up the number of fixed diff shares (fixed diff does not appear to be an option on Luckpool, however), even with a single GTX 1080.