when

when (at what time)

if and only if

when (at such time as) / when (at a given point of time) / if (supposing that, assuming that, in the circumstances that)

you can't make an omelette without breaking eggs

when the cat's away the mice will play

what you learn in your youth will be useful when you are old

the quarrel of two parties is to the benefit of the third one, which might have stimulated the quarrel / two dogs fight for a bone, and a third runs away with it

every little helps

whenever (at whatever time)