Brendan at Untimately has been talking about changing clerical magic in his game. Basically, he's adding a d6 roll, adding competency (Level/2,) and subtracting disfavor, if it exists; the spell only works on a 6, and the cleric gains disfavor if the spell works. That's somewhat similar to what I've described in Clerics Without Spells, except that I frame it as commanding spirits to obey, so I use the 2d6 reaction roll and modify it with 2 x (Cleric Level - Spell Level), and divine displeasure occurs on a bad result instead of a good one. So, my clerics have slightly better odds, don't fall into disfavor so easily, and can pray for miracles beyond what you would think of as their competency.
But that's just the differences between what he wants for his campaign and what I want for mine. I don't really want to address that. Rather, I want to focus on something he adds that I like and I think I will now steal: clerical magic takes longer than arcane magic. He has cleric prayers requiring a full ten-minute turn, which means that clerical magic mostly happens outside of combat and is mostly for support. It does mean that some clerical spells won't work properly (Hold Person.) But it definitely makes clerics feel different.
I think I would set my prayer time at 5 minutes (one move outside of combat) and keep commands to depart (i.e. Turn Undead) at the normal casting time. Also, the 1 to 4 cleric bonus spells would be immediate commands, rather than half-turn rituals.
But! This also helps to distinguish White (and Black) Magicians from both regular magic-users and clerics. These work like magic-users, except that they use the cleric spell list instead of the magic-user spell list... and their spells take 5 minutes to cast unless they prep them as cleric scrolls. (Clerics won't be able to make cleric scrolls, under this set-up; all cleric scrolls come from white magicians.) When a white magician casts a cleric spell, it always works, just like an M-U spell, but if the spell is reversed or is something like Raise Dead or Commune, make a piety check (reaction roll): on a Bad reaction, they are impious (-1 on reactions from Law or piety checks,) and on a Very Bad reaction, they become Black Magicians (and reversible spells are always cast in their reversed form.)