[El Salvador / Guatemala] Transfer from Santa Ana to Antigua

Been researching direct shuttles from Santa Ana, El Salvador to Antigua, Guatemala and found a couple that start at either 3AM or 4AM which is ridiculously early.

An alternative was to catch the Pullman bus which departs 6:45 AM which is more reasonable and seems really comfortable, arrives around 12:30 PM in Guatemala city from what I can tell.

Question - if I take the bus and say it arrives at 1:30 PM (1 hr delayed), how easy is it to get from the Pullman bus stop in Guatemala City to Antigua by another bus? I would rather not pay $60 for an Uber to Antigua but I know that's available as a last resort.

Surely there are frequent departures to Antigua all through the day including PM? I have a hotel reserved in Antigua so need to be there the same day.