When to do the 100k mile service for Pilot 2013 Ex-l 4WD?

If you are close to your miles, there's nothing stating you have to wait for the maintenance minder (if it would even register the belt). Taking care of these types of maintenance items is a good thing and there's no problem with getting it done a little early. If the maintenance minder needs to be set, the shop doing the work should reset it for you so it can restart the count. You might want to remind them to do it when you take it in, though, as some mechanics may not reset it if it isn't popping up in their faces.