The Amaro mount...

[Seraphor]

You highly overestimate leveling speed tbh. I leveled GNB from 60 to 70 in one day, and then few days for leveling until 80 with MSQ and I wasn't really fast. Right now, if you have one class at 80, all other jobs will have 100% exp bonus for 1-70 levels and 50% from 70 to 80. Plus rest bonus, pluc FC/Squadron bonus, plus additional items like earrings if you level is under 70. In fact, you will need about maybe week to level one job if your online is not very high.

By 1 day, do you mean an entire day? Like, 18 hours or so?
Because a day of play for me is about 3 hours, and I can barely fit all my roulettes into that time, and I usually don't because I like to do things besides just roulettes.

It took me 7 days to get through the MSQ to 80, and that's with more than typical playtime.
I'm leveling my secondary jobs now, two to be specific, and I'm at 76 and 73 respectively after another 6 days.
So accounting for downtime, days where I don't play FFXIV at all, which will be many once I'm over the Shadowbringers hype, and accounting for days where I don't level at all, because I'm playing end-game content, 1 level per day is very realistic.