I have setup a telnet connection.
It took 28 seconds to establish the connection,
which is 8 seconds more then the 20 seconds i mentioned before.
To be more precise:
It took me 28 sec. to reach my server from my pc at home to the server in the datacenter.
THe command i used was: telnet <ip-address> 25
On my server itself, it took almost no time.
I used the command: telnet localhost 25