Well ...
From my experience aproximately 30 seconds per level.
(Usualy i get 1 or 2 more spells)

I dunno ...
Maybe (i mean almost obviously) we play the game differently, but i mostly have to switch one, sometimes two spells when situation needs it, but never more ... on my Wizard ... through whole EA. O_o
You talk about it as if you recreated your whole build every 30 minutes ... wich seem insane. O_o

Also, there is at least one more difference between our gameplay as i see it ...

Potions ...
I never put consumables (except healing pots) to Wizard (or any else honestly) hotbar, bcs ... why anyway? laugh
- Resistance potions last to Long rest ... no reason to spend hotbar space for them.
- "Expensive" potions ... like Giant strength, swiftness and invisibility ... i use only against challenges so, no reason to spend space for them.
- Poisons i use specificly for my non-casters (wich have quite clean hotbar btw) ... Wizard chance to hit with regular weapon is almost zero anyway, so why bother.
And as far as i know, that is everything we have so far. laugh

Scrolls ...
That is different story ... i usualy forgets about them, but when i use them i mostly pick the same as are my prepared spells (since they suits me best) ...
For example i never used spells like Animal Friendship, Disguise self, or Speak with Animals ... and i rarely use spells like Hold Person, Collor Spray or Darkness (mostly bcs its still not working as it should for Warlock) ...
So yes, i do use scrolls ... either i put them to empty space on hotbar (and thrust me or not, there is plenty of free space still on my Wizard hotbar ... Cleric is a little worse) ... or i simply open inventory and use them from there. laugh

But i totally agree with you on one thing, that hotbar is tiny ... it certainly should be AT LEAST twice as big.
My personal favorite is still first build we have ever seen ... it maybe wasnt so "pretty" but it was effective.
[Linked Image from vortex.cz]


I still dont understand why cant we change Race for our hirelings. frown
Lets us play Githyanki as racist as they trully are! frown