Technically any method can happen at any time. Static encounters rare have anything other than Method 1 since it doesn't use animations (splash, rocks, grass, etc) nor does it load separate music.
The longer the animation (generally stuff that cause vblanks) the more likely a method 2/3/4.
Forcing a nature (syncing) will increase method 2/3/4 because of nature confirmation (rolling for a PID that matches the nature sync).
H (no idea why that letter) IIRC is the designation for spreads specifically for wild encounters via random chance. A wild encounter is grass/surf/caves/power plant.
The order from seed for wild encounters goes similar to this:
Which encounter slot?
Which nature? (Or Sync, or swarm, etc)
Roll PID until nature matches (many times there is a vblank here)
Static encounters, gifts, and rod are not wild encounters. I don't even think gifts have nature confirmation.
Fishing is weird cause it's like a wild encounter minus the change of the encounter occurring. I am not sure if it's lumped under H or not, but if it is, that's superficial imo.