I would draw the line at 183 days as that is half the year, and "an effect which is active half the time counts as constant," in ARM5 under warping.
In principle, there are two ways to archieve a permanent effect in an item:
Either using sun duration, 2 uses and environmental trigger
or using concentration duration and let the item keep the concentration. As you need someone to shortly focus on the concentration effect to keep it active on dusk and dawn, the last option is best avoided when keeping an important effect going (like flying with a castle... Just imagine... 
).
As you loose all recovery boni when the effect is not working for the entire time, duration: concentration is better not used.
Same is true for leaving the room, as loosing the bonus for even a second will result in the effect being useless.
So what to do to help you out with your average CrCo lab total:
Skip the room! How many times do you think you have a room full of loyal servants who are severly injured? If you are altruristic and help all the people around (meddling the mundanes?) or face the Blach Death, I would go for the target: structure version anyway.
My experiance is that even belligerent magi do not have so many wounded followers, since battle as often results in death as in injury.
So my option: Designe an amulet instead R: touch, D: sun, T. individual, +1: 2 uses per day, +3 levels: environmental trigger: base+3magnitudes+4levels. Being a lesser enchandet item you can do it in a season. Using your lab notes you can do another two next season. More time, more vis: yes! But you can use it much more deverse: On the road, the person carrying it can walk around... On the down side: These things can be stolen (unlike a room).
If you do not want to leave your idea of enchanting the room, you have to move your lab into the room first (2 seasons), enchant the room (one season) and then move it out again (another two seasons) resulting into 5 seasons. During this time you might as well have enchanted 9 amulets.
Okay, what about dat 366? Day 549? 732?.
If you are going to allow fractional accumulation of warping, at least make them accumulate a full year's worth before you warp them.
A dingus that works on Touch with multiple charges/day is far more cost-effective for anything less than a "roomful" of people. Doesn't have to be as generic as a "wand" - some Form that has more flavour. A "bed" would work, except that moving people to/from would not. Perhaps a magical cloth that is laid across the forehead?
But it's not the same feel as a room magically dedicated to recovery, admittedly.
(MM - if it's that important, maybe start a new topic? It's really straying here from Magical Rooms. Or accept that people differ - that would work too.)
Finally, i think the amulet's idea is not bad.
I liked the idea of a room for multiple purpose, but it's true that it would be very complex (+2 room, +1 touch, etceterae).
But there is one thing i do not understand:
if i target the, say, room (say that means a room with 4 walls, a roof and a ground) : that's my magical item.
Ok?
Why can't i just say: i want the magical effect work on people touching it (+1 for touch). THat's it, and, without the +2 room.
You'll see: your target is a room.
Okay, i give you this one.
BUt then, see this like that:
i'll target a rope for +- 10meters.
And give my magical constant effect (+1 touch) at it.
Then, when there are people hurt, we just attach them by feet (=> they are touching the rope).
Finally, its the same effect... and i avoid the +2 room?
I dont understand 
Or are you gonna say me the rope needs a +2group?
That would make sense.
You can. That's the Range. But that's not what you were asking before, you (and we in response) were focused on the idea of a "room" effect, and asking why the Range could not be Personal.
A single device - a wand, a castle, whatever - can have a Range of Touch, no problem - most have at least that Range.
Then, just define your Target as Individual, and decide how many uses/day it will have.
For a Form, you might want to consider the various Form/Effect bonuses that Shapes/Materials give. "Amulets" are not listed as giving a bonus, tho' imo they do have a good feel, and I'd give a small bonus (Hey, Xavi, hear that?! See!!!)
Bandage healing wounds +4 Ars Magica fifth edition p110
Hyacinth healing wounds +2 Ars Magica fifth edition p110
Ivory healing wounds +5 Houses of Hermes: Mystery Cults p137
Jasper healing wounds +2 Ars Magica fifth edition p110
Gold health +2 The Mysteries Revised Edition p33
Nothing is listed specifically as aiding "recovery", so it has to be faked, but that's a good place to start.
its a very good idea.
Amazing 
LMAO 
Nice ideas and suggestions as well as a thorough explanation there
Cheers,
Xavi