We arrived on a Tuesday & had guests arriving on Wednesday & Thursday & our wedding was on Friday. We let our guests have a casual day & get familiar with the resort on Thursday & then had a Welcome dinner on Thursday night. On the day of the wedding, we let our guests enjoy the day doing whatever it is they wanted to do, which was pretty much relaxing & spending time on the beach. As I was getting ready, they were jet sking, visiting the spa & just doing what they wanted to do so I really wouldn't worry about planning something for them on the day of your ceremony. The one planned group outing that we did was on Saturday, taking everyone to Dunn's River & then shopping.
I think you can offer things for your guests to do but don't feel obligated to plan for them since like you said, they are on vacation. The cocktail hour that you have planned sounds great. You could also turn that into a Welcome dinner, just to give everyone a little more time getting to know each other.
Basically, just take things as they come. For instance, we would all meet in the morning for breakfast at a designated time. Most of the group arrived around the same time & then we spent the day however we wanted to.
I am glad that we planned 1 group activity such as Dunn's River because it was fun but there are sooo many tour vendors around the resort, that if your guests are interested in doing things, they will definitely be able to find something to do.