Rest assured that once it's cleared by the provider, Rollbit will release the fund immediately. There is no reason or benefit for them to hold your fund further. All they do up to this point is complying to the security measure asked by their third party provider. But yes, limiting on the amount you use to bet will be a brilliant idea.
Remember that gambling is just for entertainment and never gamble more than you can afford to lose... or being held, on this case.
There are a lot of professional sports gamblers or those that gamble for profit. Many sports gamblers move money from book to book daily to get a bet down because of a line difference. The blame is on the casino for these long delays.
The keyword here is to never gamble more than one can afford to lose [or being held]. If there are a lot of professional gamblers out there [and I believe there are] then congratulation for them, they live on a high thrill. The advise will still be the same though, never gamble more than what they can afford to lose. I believe they know and apply this principle, of which become part of their success.
Regarding who to blame on this, I'll leave that topic unaddressed.