Once sperm reaches a egg, do the process start immediately or do it take a few weeks to process?

Conception: Conception occurs when the sperm penetrates the egg, this occurs a shortly after the sperm reach the egg. It can take up to 3 days for the sperm to find the egg then a couple more days for it to implant. But with both u test positive 2 weeks after the act or 4 weeks last menstrual period.

Immediately: If fertilization occurs the process begins immediately.