I'm running the Steam version using DirectX 11 and I've tried activating the Unlimited Mission Timer and it has no affect on the count down timer. Perhaps it only works with DirectX 12?
No, I run the game in DX12, and the timer option doesn't work for me.
I'm also confirming that the mission timer doesn't work. If it's DX related, I'm using DX11 when the trainer crashed. Something about currency.
Are you using the latest trainer?