Official comment
We have this feature available in Campaigns now, and would prefer that all clients move toward using Campaigns if possible. Using a Wait element you can have the contact wait until the day of the week you specify, with time and time zone honored:

It's not impossible, but unlikely that we would add new features to the legacy Date Sequences. We'll keep this open for a few months to see if it generates enough interest but most people are now using Campaigns in ONTRAPORT.