The egg white is alkaline and serves to tenderize meat. With shrimp, they can help make them more snappy. It’s one of the classic elements in velveting.
I don’t do it for longer than 30 minutes and most times I only go as long as it takes to get everything else ready, so maybe 10-15 minutes. There’s really no need to go longer than that (most times these marinades are applied to thinly sliced meat or seafood) and I never see Chinese recipes calling for longer than 30 minutes to maybe an hour, though it’s fine if you do it longer if you aren’t able to cook it as scheduled.
For example with beef here they do 30 minutes and they mention up to an hour on their article. No requirement to go past that.
They actually cite times for a few different foods in an article about stir-frying:
“ How long to marinate: Generally, at least 15 minutes is enough. For dices/sheets you might want to aim closer to 30 minutes. For something like ribs you might want to do something like 45-60 minutes. I haven’t found an upper limit for marination times, but I’ve also never tested it either.”
