All wrong. I was under the same misconception years ago.
You have UNLIMITED mil leave for a very wide variety of activities. The five year limit actually only applies to a narrow range of "voluntary" AD service (although I'm sure many employers have the same misconception you do). Off the top of my head, these are unlimited leave...
Initial training. This includes guard/reserve/regular AD. Includes boot camp/OCS, MOS training and anything else needed to get you qualified (ie seasoning orders).
Any obligation incurred by initial training. This is a biggy because it also includes regular active duty accession service obligations, ie wings plus eight years or whatever. USERRA is not just for reserves.
Normal drills and AT. You can do your one weekend/month and two weeks/year forever and it's doesn't count one day against your five years. You can do more than two days/two weeks and it still doesn't count. Pretty sure ADT is OK too.
Any involuntary active duty. Important technicality...this means the character of the orders, NOT any discussion that occurred prior to the orders. If the orders, once cut, are invol then it doesn't count against your five years. You can volunteer (verbally or formally) to be involuntarily activated and you're still protected. The employer has no knowledge (or need to know) of discussions leading up to orders being cut. I think DoD now specifies that most orders should state "involuntary" to protect the member, just to prevent employers from using their "judgement" as to what constitutes vol or invol.
Any activation, including voluntary, in support of OCO/GWOT/Title 10. This covers almost everything since 9/11.
In order to actually run your five year clock on federal orders, you would have to get voluntary orders to something which has no role (direct or supporting) in OCO. Basically we're talking war college/academy professor or maybe war college student, or possibly a few other niche jobs including some state guard jobs. Almost anything else counted as OCO (not sure how long that will last).