I played this last night with some friends, here's some feedback:
Respawn times were too short relative to the capture time. The Capture time feels about right, I figure it's just the respawn times.
(For my ulti-duo map I settled with Attackers: 1, Defenders: 4, Initially both : 6, Time to cap : 3)
Felt like the map was scarce on ammo, the two smalls were awkwardly far from each other. You'd expect for the low respawn times ammo wouldn't be a problem, but it just meant after a long fight the losing team could further dogpile with full health & ammo coming off the respawn. Players don't have enough time to recuperate after a fight, ammo is left behind because of this.
As for layout suggestions: The soldiers on both teams were not a fan of the crate combat near the point. As well as the 'clutter' in some of the combat spaces (Lightposts and such). The approach to the control point also felt a little painful from both sides, (Left and right). The drawing below is one option for the right side.
As for the crates on mid, defenders would use the extra height of the crate to bully approaching players from the left low ground. (Left of image below)
My possibly questionable suggestion #1:
Nitpick: Try to streamline these odd corners out.
Bugs:
You can enter the enemy team spawns. While this was funny at first, it's incredibly annoying to get spawn-camped as a medic. :^)
Closing thoughts:
Ultiduo is a very subjective game mode due to the fact it's so deathmatch-heavy.
I'll respond to any questions or points of contention that arise from this post, just be sure to ask! Cheers.
-Comic sans user
PS: I don't think making multiple versions of the map for a different time limit is necessary. I'm certain there's already a plugin most serveme servers use that can override the time. Just leaving this here to save any future upkeep pain.