SW:TOR launched at ~7:00 my time in December 20, 2011. At the time when I managed to get my Legacy to Level 50 it was 6 years, 7 months, 3 days and 16 hours later.
I’ve not boosted any character, but I don’t know the formula for Legacy XP and whether they changed it in the years – but it took 4x 70 (Command 97,11,5,1), 1x 68, 1x 63, 2x 50, 1x 41 and 1x 17 to get there.
My Jedi Sage started KotFE today and is in Chapter 5 (my second time), but the XP sucks – so I think I’m gonna switch to Ziost or Section X dailies tomorrow, or whatever the Conquest tells me makes sense. Trooper just hit 64 but is out of rested XP now.