Do I need to know my exact birth time?
No. A reading works without it, and the order form does not ask for it.
Your birth time only matters on the rare birthdays when the Moon changed signs that day. So after you order, you are asked for the hour only if your birthday is one of those days. Sometime in the morning is fine, and if you are not sure, say so rather than guessing. A wrong time is worse than no time.
Did that answer it?
If not, write to Sofia and she will answer you herself, the same day. You can also browse How readings work.