That is the “tick” rate of your countdown timer, you got what you asked for.
I would not advise using this method for a seconds based counter.
Expire binding has a won’t-fix accuracy bug for times in seconds; this is detailed in the expire-counter thread comments.
The method is intended for “minutes” use e.g. lighting delays, it is not accurate nor particularly efficient for seconds based counting (and we’re back to why would you want to control hot water with a seconds based timer anyway??)
If you must go with seconds, explore alternative means
