Oh also, diaphragm strain can lead to pretty serious hernias. Mine was a really minor diaphragm strain and didn't, so I was lucky. But definitely err on the side of caution. Those extra few days probably would have prevented the diaphragm strain. Or maybe wait until you can actually do a push-up... I feel like otherwise you don't have enough core strength to really run well anyways.
But yeah three weeks is totally doable