I'm not sure of the exact time, but it is usually about 15 to 30 min after the end of the service. The service start time is listed on the website.
No, one doesn't need to attend the preceding service to see the baptism. Church service begins at 10am, will end about 11:15. Baptism will be after 11:15.
I imagine they expect you too attend service and so to quote James "it's after the service".
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