In a Composer Experience, the Timer card allows you to set up a delay for the following actions.
If in addition to this card, you're also using a Delay by Time for the Action card (e.g. Show Offer or Show Template) as described here, both durations will be added up together.
So for example, if you were to use a Timer card delay event and set it to 10 seconds and then set a Delay by Time for any Action card of 3 seconds, the total delay would be 13 seconds.