Instruction: Extract information from the supporting document to answer the given question.

Input:
Question: How long after plugging in unit are germs removed from room?
Document: I bought the large air purifier and two of wall plug versions in 2007, and they're still running strong.I'm an elementary teacher and am constantly surrounded by a multitude of germs. In an effort to preserve my health, I decided to give these a try. The large unit lives in my classroom and runs 24/7 all school year long, and it definitely helps! (Healthier teacher, healthier students, everyone is happy). The two small units are plugged in my bathroom and bedroom.
This unit works great for the bedroom. I have gotten such good sleep since plugging it in the past few days. The room always smells fresh and it feels so good waking up now. The only drawback is a little bit of noise, but I actually kind of like it. Think it helps me sleep since there is no tv in there... lol
Mind you if the cat box is very dirty-- we still smell it -- but it does make a noticeable difference so long as everything is fairly clean.I'd rank this unit as follows: The noise level as moderate,The light too bright to not be disturbing unless it's below eye level or in another room,the allergy neutralizing abilities as poor, the smell neutralizing ability as moderate.
I ordered this unit, because our son had a cough for way too long. The first unit that arrived was DOA and no UV light was working inside the unit. Amazon replaced it without any problems and the 2nd one seems to work. I am not sure if the cough disappeared due to this unit or due to other measures, but it's possible that this helped. The big downside of this device is the noise. I am noise sensitive and I can't use it in the bed room at night.
:)Some people complain about these units..  saying there is low airflow through them. I'll let you in on a little secret..  it takes some time in contact with light to kill germs in the air. If the air moved too fast the germs would not have enough contact time with the light to die. Put the unit in an area where the air moves around it. Perhaps near a door or in a room with a ceiling fan that normally runs.
We just recently bought a house and it is all hardwood. We have a loft that has a full bathroom and because it is a 4th floor loft the bathroom smells on occasion. I bought this to try and clean the air in the loft and in the area of the bathroom. I got the unit and it was clearly used, it had a mark on the front of the silver guard. After plugging the unit in it began to whine like the fan of a small computer.
I have three of these things going in on room and it does no good in keeping the cat urine smell in check. Carpet was removed. I will have the room treated with enzyme after remodeling is done.
It continues to work and continues to have no issues - although my usage pattern is not 24x7, which might be the case if you are plugging it in a room in the house.Once in a while, the fan does start whining, but this seems to be sporadic and temporary - and seems to happen only as it starts.
So far so good, purchased this unit to use in our shared berthing (its a connex box with an A/C and to wall lockers and a bunk), Hopeing it will keep the air fresh and cut down on the mold and mildew and the germs. Its got a little hum to it, but its all in all very quiet. and seems to be working.
I plugged this in and it is quiet and working great. Have not used it long so I will have to get  back to you.We did install the whole house UV system but as it is not on all the time I use this in moms room.I would recommend this to anyone with breathing problems.Came promptly in the mail.
Answer: Depends upon the size of the room. This unit has to cycle ALL the air in the room through it to remove all the germs from the room. This device is rated to clean 456 cubic ft in one hour. An 8 x 8 x 8 room is 512 cubic ft of air; takes 1.12 hours to clean. An 12 x 12 x 12 ft room is 1728 cubit ft of air; takes 3.78 hours to clean.  I hope this helps. The 3rd number is the height of the ceiling, most are 8 ft tall.