You will need to edit the research.ufo file, a simple text file with explanations at the top to help you.
If you have a folder /base/ufos/ in your game, you will find the research.ufo file there. If you have a number of pk3 files in your /base/ folder instead, you will need to unpack ufos0.pk3. When you unpack it, it should create the /base/ufos/ folder with the research.ufo file.
Open the research.ufo file in a text editor. At the top is a description of what each parameter does, including the "time" parameter, the one you will need to edit.