I have done London coach on both Weds & Thurs before.
Both super easy and efficient. Think Thurs will be better traffic wise as a big chunk of people will already be on sight + the early start will help even further.
If memory serves me right, the journey is about 4-4.5 hours (if all goes well & only 1 services stop).
As you say, Thursday can feel like you’ve missed a bit, but honestly once you get there that all goes out the window. Plus you are a bit less knackered by the Monday having got an extra night in a proper bed.
Also Ped Gate A queue, which is where all coach drop offs go, I have always found a breeze. Queue moves very swiftly from Weds lunchtime onwards once the initial bunch have gone in.