I don't remember anymore, but it's a pretty basic engine made for a game jam, so probably less than 7 days. (Depends a bit on how much I cheated by reusing code from my old projects... which I wouldn't disclose even if I remembered :P) I tried importing it into GMS2 right now, it works just fine for me (I'm on IDE v.2.2.0.343, runtime v.2.2.0.258).