I try to keep my conditioning bottles around 20-22c or 68-72f. I batch carb and have had pretty good luck. I imagine the carbonation would be the safest was to make sure your getting the exact same amount in every bottle. The problem with the drops is what about bottle size. I have 11oz, 12oz, 16oz, 22oz, and 25oz, 50oz bottles. If all my bottles were the same size the drops might make sense.
The yeast in each batch play a big roll in how fast the beer carbonates. If you want to be sure it's going to carbonate properly you might think about adding healthy yeast to the bottling bucket. Some say champagne yeast works well. I don't have any experience with it. I do have a 12.5 RIS that's taking it time carbonating. 2 months and just a little carbonation. Patience is probably the best tip I can give you.