I had a job where we had an old fashioned paper office calendar. If we wanted to use PTO we simply wrote the days on the calendar. Our boss only wanted to know if multiple people from a workgroup were leaving on the same day or if it may cause issues (and he trusted us to figure that out). It was glorious.
My wife is only approved to take PTO once they find someone to work the shift. And they will not even try until the month before. We buy plane tickets 3-9 months out.