The support halfway up the drop looks to be supported by the track as much as it is supporting it (from the look of the support angle), so it probably doesn't matter which is built first, because when the coaster is completed they'll work together to brace.
I would imagine this part of construction has to be planned with the weather in mind, but because it's built to withstand a 20 ton train pass by that it's pretty overengineered at this point and could happily sit there without the support for a while.