The right answer is 5 - 10 seconds.
The heartbeat check according to ACLS should not take more than that.
The steps for checking your heartbeat are:
Have a watch. It will be used to measure your heart rate.Choose a place to take your pulse. It is better to choose either the neck or the wrist.
Place your fingers so that you feel your heartbeat. Choose a duration for the measurement (5 to 10 seconds).
Start counting.
Multiply the number by 12 if you counted for 5 seconds (by 6 if it is 10 seconds).
The normal frequency is between 50 and 80 bpm