It is 9:58am and sof zman tefillah is 10am. What do I do? Say shmoneh Esteh fast to finish by 10am or say it slow and finish after 10am.
You should say it fast and finish before the end of zman tefillah.
Mishna Brura 89:5, 58:5, 110:1, 233:14
cf. Aishel Avraham Siman 89, 232