Does this effect your 5 second timerFollow

I dont know how/if this changes when specced discipline, but for holy priests, you only ENTER the inside 5 second regen space when a spell has gone off. Since u are cancelling a greater heal, that 2 seconds or whatever of precast does not count as an actual cast of a spell (since none was casted obviously) and therefore you stay out of the 5 second rule. (which is good)

U regen mana no matter what, whether a spell goes off or not, its the RATE at which u regen that changes. If u cast a spell, then u regen at a certain rate (in combat rate if u will). If u wait for 5 seconds, or proc something that will make your next spell cast free (i.e. inner focus or hoy concentration) you will regen mana at the normal rate (out of combat rate if u will).

Because priests rely greatly on spirit (well at least pre-wotlk), cancel casting becomes a highly effective tool. Imagine you are at 60% mana, you ahve hots on tank, you pop a spirit trinket or something and then pop inner focus. U cancel cast that heal for lets say 7 seconds before finally allowing it to go off. Then you start cancel casting another heal and let it go off 5 seconds later. That is a full 12 seconds that you got of 100% mana regen (plus trinket use).

Is a very effective way for priests to regain mana and pace themselves. not as cool as divine plea for pallies but given the cost of priest spells, its quite an interesting strategy

same with concentration..

Only spells that actually consume mana trigger the 5 second rule.