How to detect how long a player has been holding an item

I'm trying to detect how long a player has been holding a specific item. For example a regular stick. If the player holds it for 100 ticks then a procedure runs. If the player switches from the stick they still keep the ticks they were at before they switch. For example they held the stick for 40 ticks then switched items, then switched back, the timer would resume from tick 40