As per title, make divine might/shield an instant cast. It's abit niche and hard to use, so why not make it instant like barbarian rage.
Okay, I started posting this as a meme in the Discord initially to annoy some people with.
But in all seriousness, yes. Divine Might (DM) should be instant cast (aka. free action) . Divine Shield (DS) not so much. I will explain why.
First we have to understand how the duration of both feats work. Each scales with your CHA modifier. And since both feats require you to have at least 13 CHA you would assume them to last only 1 round.
There we have our first, minor difference between the two. The effects are applied instantly when the feats are used and the duration begins ticking down the next round. This is where DS is already superior. You profit from the increased AC upon the cast. DM instead only benefits you once you start swinging.
Second, the effects are (obviously) very different. I always say, to be not hit at all is better than to be hit for little. That is why Improved Expertise is always so good for dedicated "tank" characters who's only purpose is to keep the attention of enemies and not die while doing so. And the same goes for DS.
DS giving you hard AC and not DR makes it much more potent than DM which does not give you AB but instead divine damage according to your CHA modifier.
So DS is strictly better than DM.
Now if DS was changed to a DR according to your CHA modifier instead of hard AC? Then that would make it more in line with DM. But the way both feats function now I would advocate for making DM a free action but not DS.
Now someone could ask : "Why make it a free action at all?"
Simple. Because it is somewhat of a gimmick that you have to specifically build for and currently it is a gigantic sacrifice for your action economy to use, especially in PvP.
And with the currently rampant running barbarians getting so much more than any other class from a feat and furors all of them get for longer and with nearly no drawbacks at all ... it would ultimately just help DM paladins in that department and bring them in line.
Paladins are pretty potent imo and while this would certainly be a nice QoL change, it's also a significant buff. With eagle's splendour and aura of courage even a paladin who has minimally invested in CHA can get to decent modifiers. DS and DM are also undispellable and do not provoke AoO. I personally think they are very powerful but clunky feats to use as is.
My alternative suggestion is to perhaps offer some way to expend more Turn Undead uses for a longer lasting DS/DM. (So burns 2 TU charges for double duration, etc.)
The alternative suggested by Nazey would absolutely help out. Maybe a custom command for how many uses of Turn Undead we want to use?
If that is possible it'd totally equalize the problem of the action economy DM builds suffer under as you would still have to spend a round but could at least direct how long it lasts.
Notice how I only mention DM and not DS.