I think, that would be a good enough fix. There should be no delay on divesting, though. It can always be, that one really needs to divest now. Adding a delay of say, 15 min on Investments would be good. There is no reason besides gambling why you couldn't wait this long for your investment to count.
It won't solve much for mechs.
Anyone will divest when profit will go to 3k or 4k or 5k and nakowa comes to gamble

Everyone will invest when the profit is down (15 min later or before does not change much).
And it will take months for him to recover his loss, unless he invest more now.
I am personally maximally invested at this point. Plus, everytime nakowa has come by, it has consistently ended in the site losing 1000s of bitcoins - it has been at least 7 different occasions now. It is true during the latest session the profit for the site went between +6000 and -5000 ending at -3100. Some made profits by divesting whenever there was a streak of losses for nakowa (and thus profit for the site) and then reinvesting when site profits went inevitably back down. That is why passive investors likely myself have losses magnified out of proportion to the site. Successful investors/traders diluted passive investors profits on the way up and magnify it on the way down.
Hell even Dooglus divested when the sites profit was up to 3000 BTC today locking in profits and then magnifying losses of passive investors down to -3100. It seems like you do need to run a bot to actively invest/divest for swings in site profits or just be around for those times when nakowa is online.