reusing a timer watcher with different 'at' attribute

Hi,

I noted that the 'at' attribute in a timer watcher is 
read-only.

This makes hard to reuse the same watcher several times
with diferent values for it.

Does it "have" to be read-only?

How much does it cost for an application to destroy/cancel
a timer watcher and create a new one a few times per second
instead of reusing a pre-existent one?

I am using timer watchers to delay proccess.
There might be 2 to 60 concurrent timerwatchers
and they may delay from tenths of miliseconds to a few seconds.


Regards,

Raul Dias