The staking warmup period, is the amount of time a user has to be staked for before receiving any rewards from a rebase. This is important for TVL and prevention of abusing the rebases, where people will stake momentarily before in order to yield the rebase rewards with no intention of holding on to their rewarded $RUG. This serves no benefit to those that are holding throughout multiple rebase periods, as it dilutes their yield.
Note - This does not change the rebase epoch period, which is currently set to 8 hours.