The primary reason I have a problem with real life timers stems in part from my group size. On any given night I have between 8-9 people around the table. The simple logistics of having 8 characters means adventures just take longer. But, even when we have smaller groups, we still take longer than seems to be expected.
Just as an example, I ran my group through Darkest Hour which is "designed for a 4- to 5-hour convention-style timeslot". My group finished it in 5 sessions. As designed, players will have 1 set of action dice and have 1 use of per session abilities for the entire adventure. At my table, my players get 4 additional action dice refreshers and 4 additional uses of per session abilities to cover the same exact adventure as the group sprinting through it during a 4 hour time slot.
So why should a large, slow group get about 5 times the resources to complete the same adventure?
Hourly timers run into other problems. Just about everyone I game with are friends away from the gaming table, too. There is going to inevitably be time lost as people BS and otherwise get caught up on the previous weeks events, or we'll wait while someone orders pizza or whatever. While we are in this "kinda sorta playing" phase what happens to the real life timers? If we start playing at 6:55, does the guy get an action die at 7:00 because the GM hasn't handed out dice yet? What about when a couple people step out to pick up pizza for the group and those of us left behind are just discussing different aspects of the game?
Real life timers seem to operate under certain assumptions about how people play the games which don't seem to actually be true in real life. In general, real life timers get messy and I would rather not have them at all.
At the other end of the spectrum, there's some potential in making action dice less alarmingly powerful, and thus maybe better suited to use as plot lubrication through regular granting. For one thing, adding to damage has always been different ftom adding to checks. Just because the contribution reletive to the base is so much larger, and because as yo note, its a place where magnitude matters, while checks an saves are mostly looking for threshold.
That's a couple things I had noticed, too.
Adding action dice to skill checks of a d20 vs adding action dice to damage of a d6 to d12 gives a markedly higher percentage return on the expenditure.
Also, spending an action die to heal? You get 2 wounds. Spending an action die to cause wounds? You get whatever you can roll out of it which will almost always be at least 2.
I've contemplated removing the action dice ability to add damage on several occasions now and limit their expenditure to d20 rolls.
I've also contemplated swapping the action dice cost for critical injuries, which would now require 1 action die, with critical hits, which would now require at least 2 but maybe more action dice.