There is software for general contracting that can estimate labor hours. Nothing specifically for PV work that I know of. The software for general contracting is set up for large projects though, it's going to be too expensive and overkill for most PV projects. From what I have seen most PV contractors just set up their own spreadsheet based on their experience to do the estimates. FYI, labor hours are always an estimate, experience turns a guess into an estimate but that's as good as it gets.