the fact that the judges even asked for a response to a mandamus petition is a rare occurrence – usually mandamus petitions are just denied outright. same goes for oral argument.
argument could go from ~45 mins to 2 hours depending on what the judges do – the crooked H hearing went well beyond 15 mins per side last week.
decision coming down is hard to predict, but since they scheduled oral argument within a couple of weeks of getting the briefs, my guess would be by end of June / early July. this is total speculation, though. it could take days or months – really depends on the panel.