I've done EMH than park hopped multiple times myself. If you are going between HS and Epcot, then it is rather doable. All hops are doable, but any hop that includes MK is probably going to cost you quite a bit of time. Morning MH is very worthwhile in the summer! Hopping might not be worth the time. It is a very personal choice.
Via WDW transportation, morning hops often cost us half an hour, often close to an hour: gate to gate. (exit of one park to INSIDE the gate of the 2nd.) Many people will say they hopped in 15minutes- but they are often only counting RIDE time. They often aren't counting: the time it takes to walk to the bus stop, monorail platform, waiting for a bus/boat/monorail, load time, the walk from the bus depot/dock/monorail platform, waiting for the TTC monorail, bag check, or font gate line. Phew! I should add again - Epcot to HS is the exception. (*see below)
We also tried EMH before late breakfast ADR's. I liken it to swimming up stream. WDW transportation is trying to move as many guests as possible TO the parks, not the reverse. We've often waited 30+ just for a bus to pick us up.
Most of the time, we now use our own car. If you have your own car, then hopping is quite a bit faster. A GPS is useful. No matter what, MK is ways northwest of the other 3 parks. With a car, we can usually hop AK to/from Epcot/HS in about 15-20 minutes - gate to gate, depending on where you park and entrance delays (bag check, etc.)
* One trip, we were ENTERING the Test Track pre-ride design room when our TSM FP went live. (the start of 1 hour window) As soon as we got off TT, we kept a rather brisk pace ALL the WAY to TSM, and JUST made it before our FP expired! Phew! It was quite a haul!