Seems about right if you use a second builder for most of the time and waste very little of those builders’ time. I would also assume a player would build 2x TC20 to maximize possible free 5* pulls.
Without calculating the Farm/Mine/Watchtower times, I get around 582d of builder time; dividing by 2 leads to about 291d.
I will say that either a 1 year subscriber to VIP or a 2 year f2p player is a fairly large amount of dedication in order to be able to possibly trade in 1-2 vanilla heroes for limited heroes per year (and no guarantees). Some have requested to be able to build 2 HA, which is fine to help increase the volume of tries per year. I feel that this solution or cutting the retrain time in half are reasonable adjustments to make (the latter is more f2p friendly).
Of course the other levels might need a bit of work; the odds on HA7 for higher star trainers should be improved to increase that level’s utility in my mind.
Note: I am mostly posting to say you are right on the timeline of attaining HA10. Added my feelings regarding the output of HA7/10 as more of a ‘while I am here, I may as well post a bit more’.