Certainly, its reasonable for a delay in options being available while market makers prepare to make the market for those options. But shorting? Day 1, the shares are trading and available to borrow to sell to short.
Are they actually? How many intermediate steps are involved in finding shares to borrow for a short? I imagine they have to be transferred to some central depository with the feature, for a start, and that takes 2-4 days
Your broker will locate and borrow the shares from an available pool (such as other clients' portfolios), sell them on your behalf, and hold the cash. They don't have to go to the clearinghouse.