Once the amounts get large, the rebate stops being the most important term on the page. Several operational limits start to bind, and they are easier to check before you build a balance than after.
Withdrawal caps. Daily, weekly and monthly limits that look irrelevant at small stakes become the binding constraint at volume. A site paying out a fixed maximum per week will take months to release a large balance, and during those months the balance is sitting in your casino account where it can still be staked. Ask for the caps in writing, and ask whether they are lifted at higher tiers, since some programmes use exactly that as a perk.
Identity and source of funds. Verification is usually triggered by amounts rather than by signup, so the checks arrive precisely when you have something to withdraw. Source of funds requests, which ask for documentation of where the money came from, are normal at large sums and slow. Complete verification early rather than under time pressure.
Manual review. Large payouts are commonly held for human approval even at sites that settle small ones automatically. That is the usual reason a headline payout time does not apply to your withdrawal.
The VIP host. A host is a retention role. The offers a host can extend are discretionary, unpublished and adjustable, which makes them impossible to price and easy to over-value. Anything worth having from that relationship should end up in writing.
Reloads and level-up credits. These usually carry their own wagering requirements, and a requirement is what turns an amount into a condition. Read them the same way you would read a welcome offer, which is to say, never on the strength of the headline alone.