SpecOps Stealth Patrol

Enter your name as "ROCKSTAR" it might work. It works on Ranger Elite (Another Specops).

Wardy

I dont think there is a way to get infinite time without using a gameshark.
Once you learn how to move and where you have to go however, you will usually be able to accomplish the misson within the time limit.

As for the Rockstar cheat, all you have to do is this: when you start a game and it tells you to enter your name, enter the word ROCKSTAR. Accept the mission, select your rangers, give them everything they will need, and begin the mission. Once you are in the field and can see your rangers standing there with their weapons, pause the game. In the pause menu, you will see the option "Invulnerabiliy" Highlight the word "invulnerability" and press the X buton. Then unpause the game. You wll now be invincible.

Even though I haven't played this game for years, I think "Rockstar" does work. I used to have this game, and I had to input cheats (the game is way too hard!).