The real risk is a chain: if either sale falls through, financing is delayed or a condition is not satisfied on time, a same-day close on the other property can collapse with it. Building in even a short buffer between the two possession dates removes that dependency.
Bridge financing exists for exactly this gap, letting a buyer access equity from the home being sold before that sale's funds actually land, so a lender conversation early in the process is worth more than trying to force two closings onto one date.
A same-day close is possible, but a same-week close with a buffer is usually the safer plan. Get your hand-reviewed valuation from Joel Dyck.