The closest to the Sands is in Plaza La Isla. Actually there are two located there. I'd say the distance is about 1.5 km from the Sands.
The market located in the Sands has its own coffee shop with various kinds of cof to fee drinks. It opens at about 7:00 a.m. I was in Kukulcan Mall this past week but I don't recall seeing a Starbucks. It is a 10-15 minute walk to La Isla to reach the Starbucks. I would try coffee shop in the Sands first.
As said, the Royal Roast in the Sands has very good coffee, I believe they open at 8am and close at 10pm.