Most of the inventory examples .... You say ....
Most of the inventory examples have an inventory, a place to store things, usually an array.
You are still on a point that lacks one.
I will be happy to help, but at this point you have (besides a graphical representation, that should be a tilemap) nothing in place. So helping at this point will be rewriting one of the many inventory tutorials.
So may i kindly suggest that you, based on the many excellent inventory examples, code your inventory system. Without worrying about the 'delay' yet. Adding the delay, as in your question, i will be happy to help with.