...usually
regardless of whether I'm on a practice approach, pop-up, or pre-filed
IFR flight plan. There's no clearance limit there...

If you are on an IFR flight plan, you already have a clearance limit.
It was given to you when you got your clearance. "CLEARED TO FooBar
International via..." That doesn't get invalidated by an approach
clearance. If you are VFR, the approach clearance doesn't give you a
clearance limit, and thus does not make you IFR.

Jose
--
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