I’ve also sent in an email to the Eventide support,  here’s the response:

Sorry to hear you are experiencing issues with the speed that Programs load on the H90. We have tested this extensively and have determined that the Programs will load at an acceptable speed for live performance and other applications. Below is some further information:

• There is a tradeoff between the spillover time and how quickly you can expect Programs to change.
• If your spillover time is 30 secs, and you try to quickly load Programs within that 30 sec window after the first Program switch, you might have slower switching times.
• Programs will switch faster outside of the window of the spillover time.
• If you need to change Programs quickly, reduce your spillover time or turn spillover off.
• We haven’t measured any difference between the pedal receiving MIDI PC messages and switching on the box itself