Is there any way doing a /timer without showing the "activated/halted" information in status window?

Yes, you can silence most commands by adding a . in front of the command. It works also for the timer command.

.timer-without-warnings 1 1 echo -s command executed.

Well, it's not really infront of the command is it? :P

Inbetween the forward slash and the command.

/.timer 1 1 echo -s Silent timer.

In a script, the / isn't required, so
and are the same.

He was talking about in front of the command! :P the last op said in front of the command instead of at the beginning :P

Lpfix5 is correct, nonetheless the usage of the "/" doesn't really matter, some use it some don't it comes down to personal preference.

I'm not disputing what Lpfix5 says, but as I see it, there are actually two commands in the line. The first is the command that starts the timer, the second is the command that is executed when the timer ends. Using this as the basis, then the . is in front of the command -- the timer command.