I’d allow roughly 30-35 minutes for Skyliner DHS to CBR then CBR to Epcot IG. (If they’re going to enter DHS before they do this, they’ll need hopper tickets and to start their Epcot excursion no earlier than 1:30 PM since they won’t be able to enter Epcot until 2:00. If not entering DHS, no hopper needed but they’ll need a park pass reservation for Epcot.) I’d then allow 20 minutes to enter Epcot and walk from the IG through the park and exit to the monorail station. Then 15-30 minutes for the monorail Epcot to TTC, then another 15-30 minutes for monorail from TTC to MK (depends on how long they have to wait to board the monorails). So I’d allow a couple of hours, and I would not have a tight deadline such as an ADR or ILL$ or Genie+LL at MK. I would look at it as a fun excursion!