There is no single best time for every business, but there are strong patterns. Immediate requests work well when the outcome is visible right away. Delayed requests work better when the customer needs time to evaluate the result.
Use immediate timing for instant-impact services
Detailing, dental cleanings, restaurant visits, and salon appointments usually convert well with same-day requests.
Use delayed timing for longer-term results
Repairs, moving, and some medical services often perform better with a next-day or two-day follow-up.