Can Grandmasters beat computers when given time-odds? For eg., if a grandmaster is given 10:1 time odds, will he be able to beat a computer? For eg, if the GM is given 120 minutes for the entire game and the computer is given 12 minutes? If not 10:1 times odds, then please mention what time odds would be required for a GM to beat a computer.
Yes. A grandmaster or a team of grandmasters can hold a draw or win against an engine when given time odds.

I think that there is a minimum time control at which an engine can perform equally good or better than a grandmaster (without time odds). I guess this number is somewhere around 2 or 3 minutes for the whole game.

Let's say for simplicity that it is 5 minutes. So the engine needs 5 minutes for the whole game to perform at a decent level. Now, how many minutes does a grandmaster need to match an engine that has 5 minutes?

It depends. In the opening, the human player needs to be well prepared. Otherwise, it doesn't matter too much if the player has 5 or 50 minutes for the opening part. In the middlegame, my guess is that the player should avoid sharp positions and go for calm waters to reach an equal or slightly better endgame. Try to keep a healthy pawn structure and find long term advantages.

The endgame is where the player has a good chance of holding a draw or winning the game. In general, the more time for middlegame and endgame, the better. I would say that around 20 minutes for the opening, 40 minutes for the middlegame and 40 minutes for the endgame should give the human player a fair chance. That gives a 20:1 ratio (engine has 5 minutes).

This is a rough guess and it needs to be tested in practice. Such a test would be interesting! If the player has a chance to practice against the engine, then the player will of course be even better prepared for a match. I guess such a preparation is pretty normal for human versus machine matches.

My guess would be that the engine's strength grows faster per additional minute than the human strength per additional 20 minutes. When the engine has 15 or 20 minutes for the whole game, it might already be difficult for the human player to match its strength, despite having extra time. Yet, a team of grandmasters should cope pretty well (given time odds).