The thing i get sad about is that they are tonning down Asahi service a little in the anime (but it's a bit inconsistent) tho.
Also, sadly we all know girls like her never wins in those types of shows, the winner, if any is always the obvious one and/or the first he met, in this case the tsundere that hurts him for no reason, and only at the very last chapter of the manga...
prolly less, at 5am they do need to walk into the shed, search something, get stucked, think about how to get out, then actually breaking boards. maybe around 10 minutes tops since japan sunrise is actually 5.30 am on april/spring.
Also, it depends on the wood, i mean, nobody said the woods were decaying there so it could be that he had to take out all the nails, or most of them