Think the 5 second rule is a very good one. It's not dissimilar to the situation when a maul stops moving. The ref makes a judgement call and the SH has to get on with it.
We all have seen plenty of occassions when a SH is fecking around at the base of a ruck to kill time when the ball is clearly available. The ref now has the discretion to make him use it. It's pretty obvious when to call it.
Pleased with all the changes in fact. 23 man squads is a very good call.