I figured it was further out. It has been long enough since they did in TD1 so I don't remember precisely but they raised it a while after release. It seems like it was along side a patch update.
Like the OP is eluding to, whether or not to grind WT4. I initially thought about going ahead and grinding a couple more mules up just in case but I decided that I may do one like that but will wait on the others to play through with friends.
*edited: I found the release date of WT5 in TD1, it was released with the 1.5 update for the PC on November 22nd 2016. The game was released in March 2016. So, 7 months?!?