SMS booking confirmation to have an exclude if after enrollment date

The workflow action Send class SMS doesn't support a condition or trigger to exclude enrolments after the start date. This functionality isn't available in any of the other workflow actions either.

what this causes is that if you enrol someone in a workshop after the date it will still send an SMS. would love for it to also have the ability to 

send SMS 1 hour after enrollment excluding if after course start date.