Unlimited time:
Load or reset the game, then execute the following BASIC commands before running or restarting the program. 

POKE 34711,234
POKE 34712,234
POKE 34713,234
SYS 33393,173 
Unlimited time (alternate):
Load or reset the game, then execute the following BASIC command before running or restarting the program. 

POKE 34686,173 
Invincibility:
Load or reset the game, then execute the following BASIC command before running or restarting the program. 

POKE 44049,96