When they're ready. When you're not. There is no such thing as an atheist in a foxhole. The easy way is always mined. When you have secured the area, make sure the enemy knows it too.
Incoming fire has the right of way.
No combat ready unit has ever passed inspection. No inspection ready unit has ever passed combat. If the enemy is within range, so are you. The only thing more accurate than incoming enemy fire is incoming friendly fire. Anything you do can get you killed, including nothing.