field substitutions - Would this work?

There have been many discussions about the use of field substitutions, especially when the fielder goes off and then returns after a short time.

Would the following work?

A substitute can not be brought on until after a certain amount of time (1/4 of hour?) or so many overs (4?), (whichever is the longer) after the fielder has gone off. In relation to the overs part, perhaps this should start after the current over has been bowled if the fielder goes off during an over.

This would have to be applied all the time, even it was obvious a fielder was injured.

I would like to think the fielding captain would think twice before allowing a fielder to go off so decrease this occurring.

There may be a couple of things to 'iron out' like, what happens at the start of a new day if the 15 mins. or 4 overs havn't been completed? or will a substitute be allowed immediately if a bowler goes off during an over? certainly not if the bowler goes off after an over has finished.