I think 5 years is a good time period. It's long enough to prevent it from being spent all at once, yet short enough to have a strong impact on progress. It's important to note that this doesn't mean the funds have to be spent in 5 years, it just means it will be possible to do so, if that's what stakeholders want to do.
I also agree that HBD haircut calculations shouldn't take into account HBD held by the hive.fund account, so we need a modification to those calculations as part of the release.