timing on 87 camaro

how do you know car is in time before starting car?I changed the cam and want to check timing before i start it. Will it hurt motor if i start it and timing is off?

No, but the car will run a bit bad, depending on how badly the timing is off.

Advancing ignitioning timing too much will cause knocking which is harmful to your engine. So yes, depending if it is retarded or advanced and by how much. It could be harmful.

how do you know car is in time before starting car?

By marking reference points on the dist, mating surface, and rotor when you took it aprart and putting it bak the same way.

Pull the #1 spark plug. Put your thumb over the hole. Using a1/2" drive ratchet or breaker bar, slowly turn the engine over (clockwise looking from the front) until you feel the air trying to blow your thumb out of the hole. Keep slowly rotating while watching your timing mark. when it reaches 0, stop. set up your distributor & oil pump shaft so that when you drop the distributor in the rotor will point to the #1 terminal on the cap. Install the cap and wires. Triple check the wires to make sure they are going to the right plugs and cap terminals. Start the car and set the timing like normal.