not really, too many variables, most of which are out of our control.
Calculating T would be affected by number of transactions required to seek through, and that's about as far as any reliable variable we have.
But T is also affected by the following:
Unexpected Network latency, network load, # hatchers in the network, the performance of those hatchers (hardware specs), degradation of hatcher performance due to fragmentation of either RAM or HDD
If you really want a formula I can give you one, but it would be complicated, inaccurate most of the time, and of no real consequence or use.
do you have any sort of ballpark figure....you think may apply, eg 1,000,000 transaction, of "blockchain" size.....
I guess this may be something people want to know long term that it does not become exponentially long or to a power.
eg some sort of t = f(ax^bn), or is going e^x, where bn and x is positive and >1, may be fatal, unless sorta equivalent to mores law, which is sorta the HD space growth assumption for BTC (putting electrum to one side)
so I think the order of the equation is all that is needed, not the detail.