What do you think is the latest viable timing for the current iteration of heavy tanks?
Personally I actually think the current timings are fine, with some minor tweaks needed (like a slight cost increase for the IS-2, a manpower increase for the Pershing as it's only 600mp currently and perhaps some extra fuel too, and perhaps Ostheer Tiger to T4 and give the Ace a cost increase to Tiger II levels). One other solution could be to delay their peak performance slightly by moving some of their performance (like reload) from vet 0 to vet 2 or vet 3, giving the opponent a bit more time to get out counters, while keeping most of the shock value and easier army composition fitting at 9 CPs.
Heavies can indeed come early, but it's usually kind of evident that the enemy is getting one and/or the result of a one-sided match. Now there is finally a reliable way again (looking back at vCoH) to end a dominating match early (see Noggano's 16 minute Pershing versus HelpingHans in a match where he had 35-50 fuel income for a majority of the time), because mediums are not incredibly reliable at overwhelming an opponent at that point due to how potent ATGs/snares/mines can be at fending them off.
I personally like how heavies are now viable across all gamemodes, and how they can serve a role again (bringing overwhelming power at a point where you got the opponent cornered). Mediums still have a role in shock value (a ~11-12 minute medium can sometimes be more devastating than a 16 minute heavy, see VonIvan's 11 minute Sherman vs PFC) and they can still be used en masse to great effect on certain maps (like General Mud). And there is still always a good amount of risk involved by putting all faith into a single unit.
So personally I would opt for some small tweaks to performance and timing (cost), rather than pushing their CPs up again and potentially making them come too late in teamgames again.