Hi Micaela -
You can do this using the "Advanced Wait Properties" menu (by clicking the gear icon in the wait step). You can enter a specific amount of time you'd like to wait, along with the time you want the wait step to end. It's worth thinking through the different use cases and exactly how what you want to handle somebody who meets the trigger criteria at say, 7:59 AM or 8:01 AM, but you could start with something like this:
This documentation should help: Use a Duration in a Wait Flow Step - Marketo Docs - Product Documentation
What you want to do is specify the time you want the wait step to end. Click the gear on the wait step in your flow tab, then set your parameters as you normally would. THEN choose a time that the wait step will end on.
Your duration is 2 days, and you've set the "Must End On:" field to "Any Day" Then you select 8AM as the time.
What this will do is push the flow step out to the time you've specified. So if it's 5PM on Friday and I trigger your smart campaign, I will receive the email at 8AM on MONDAY.
5PM on Sunday would fulfill your 2 day wait, and then the 8AM constraint pushes the wait until the next time 8AM rolls around. Make sense?
Think of the wait step as a gate. All of your campaign members wait at the gate until they've hit all of your thresholds. Once they've waited for 2 days (or whatever duration you've set) they then also have to wait for the time. Once that happens, the gate opens and they can proceed. Make sense?