While sailfish do migrate up and down the Florida coast, I don’t think you can time or pinpoint their movements weeks in advance. Their movements are going to depend on weather patterns and bait movements – just to name two factors.
In March, the hot bite may be further south, or it may be in Stuart. Since the sailfish bite can conceivably be good anywhere along Florida Southeast Coast, I suggest you plan your trip on other factors like the captain or type of fishing desired.
If you have a favorite captain, give him a try – it's a known quantity. Or, you can plan your trip by fishing style... In the Stuart area, they do a lot of trolling because it allows them to cover more area. Further south in Miami, for example, where the sailfish alleys are rather narrow, captains prefer to kite fish with live bait.
If you are intent on pinpointing the hot bite, you’re going to have to wait until the last possible minute, and even then, you may hear those dreaded words, "
You should have been here yesterday."