With no haste, counting the HF GCD and a smite as a GCD equivalent, you can fit in 4.6 GCDs during the 7 sec HF debuff duration.
With the glyph, one of those GCDs are lost to the HF cooldown, the rest can be spent smiting.
To fit in 4 smites into that 7 second interval, you need to take those 4.6 GCDs up to 5 GCDs, which require around 7% haste. Easy. Everyone has this!
To fit in 5 smites you need a lot more haste. But as we will find, haste is actually a bit irrelevant, interestingly enough.
So I will calculate three areas of interest.
- Damage done in the first 2 second interval
- Damage done in the next 7 second interval up to the last smite. All this will be boosted by the smite glyph
- Damage done in the last fraction of the 7 second interval. This will not be boosted by the smite glyph since that smite lands after the debuff vanishes.