So I wanted to test shifter before I reincarnated a character to one. Oh boy!

---- First the obvious bugs -----
No passive bonus from shift type for shifters
The ability score from the 2nd core enhancements for shifter does not add to attribute points.

Well that will delay my shifter reincarnation.

--- But now for rage ---

I get that you changed the rage so having different types of rage didn't add time to each other.
But isn't the base time supposed to be 30?

Experimenting with a shifter .....

19(23) (+6) Con -> 42 secs
19(26) (+8) Con -> 54 secs
22(26) (+6) Con -> 54 secs
22(29) (+9) Con -> 60 secs

Shift Rage length appears to be 6 secs + 6 * con bonus secs ( Con while raging points count )

So I switched to my druid bear ....

45 Con (+17) 49 when raged (+19 )
Raging got me 120 seconds ( 6 secs + 19 * 6 Secs = 120 )