create a triggered survey

I have a main survey that we bill sent out three times a day to each participant of an experimental study. I want Qualtrics to send a further survey 30 minutes after the participant answers the main survey (this means that this second survey should be sent at a personalised time for each participant, depending on when they reply). However, triggered surveys through the action tab can be planned just by days (1 day after, 2 days after…), and not by hours (30 minutes after, 1 hour after). Any insight on how to solve this problem?