Hi

I need to book several meetingrooms as administrator.

we have 20 Meeting rooms, and I wont to Lock the room for booking fra a date to date.

eks.

from 08.09.2015 8:00 to 10.09.2015 17:00

You can block from the OWA or outlook.

Hello! 

It not default functional Exchange. It is art-task :)

Example:

1. Create in "Task manager" task, that disable access to room mailbox for several users. Start 08.09.2015 8:00.

2. Create in "Task manager" task, that enable access to room mailbox for several users. Start 10.09.2015 17:00.

Hi,

For Exchange server, we can use policy to lock down the resource booking options. For your reference:
http://blogs.technet.com/b/exchange/archive/2007/05/14/3402515.aspx

For your question to lock down resource mailbox from 08.09.2015 8:00 to 10.09.2015 17:00, we can use policy as I mentioned above, or book every all day meeting first and reject conflict request, or create an recycle meeting as your expectation.

However, would you please post more details why block down meeting mailbox during this time range?