I wondered if this template allows for the possibility of putting more than 1 project to view on its timeline. I was asked to try out this free template by my supervisor who wants something the team can access for multiple projects, each with different but sometimes overlapping milestones within them. I need to know first if it's possible to put more than 1 project on this template. Any advice?
You're making the assumption that we all here know what "this template" or the "project timeline template" is in the first place.
Speaking for myself, but probably most others, there are a LOT of free templates out there. Since it is simply a free template and therefore presumably not proprietary, could you post a copy so we could take a look at it. And ideally, so long as there's nothing proprietary, have it be a copy that has some actual data in it. That would help us help you.