Delta is the number of seconds since the last frame. So to get the number of milliseconds, you can just do delta*1000

Check out Xnconvert, it’s completely free and was made for things like this. You can do a bunch of different actions on a set of images and specify where and how to save the output files.

It’s definitely possible if you’re going back to Windows 2000, but I don’t think commercial engines are going to get you there, you’d probably have to use the Win32 api directly (or something like SDL) with a software renderer or a very old version of DirectX. I’m not sure about Windows 95 and 98, it might be possible but I don’t have experience going that far back. I’m pretty sure it’s not going to be possible with Godot 3 or 4, maybe with Godot 2 or older versions if you can still find those online