Hi @BMP ,
Not the best of the solution and probably you would have already thought about it, we can have two flows as below.
Flow 1
1. This flow will have Microsoft Forms trigger.
2. Create the certificate and save it to one drive folder.
3. Update certificate path and form submitter's email ID in an excel.

Flow 2
1. This flow will be scheduled at 15:30.
2. Iterate through each rows of excel and send email with certificate as attachment.
3. During each iteration, delete current row from excel after sending email.
