All right, so I'll assume that this is talking about the infinite loop at the Battle Resort.

Let's steal Reddit's calculations. :P

>It takes about 21.10 seconds per lap using a mach bike and the route has exactly 256 steps.

So that boils down to 12.13 steps/sec.

Reddit

Pokemon in the daycare gain 1 XP per step, or about 12 XP every second in the loop. So let's look at all the leveling curves, assuming you put them in the daycare right after hatching or whatever.

Growth Rate (XP Lvl 1 -> Lvl 100) = seconds to max

- Erratic (600,000) = 49464.12 seconds
- Fast (800,000) = 65952.12 seconds
- Medium Fast = (1,000,000) = 82440.23 seconds
- Medium Slow (1,059,860) = 87375.10 seconds
- Slow (1,250,000) = 103050.29 seconds
- Fluctuating (1,640,000) = 135201.98 seconds

Growth Rates

Now friendship. It's erratic, but it Bulbapedia says ~50% chance for +2 0-199, +1 200-255 every 128 steps

So I'll deal with those separately. Using the same data,

- 0 - 199: 1/2 * 2/128 (happiness/steps) = 1/128 (happiness/step), or 25600 steps (2110.47 seconds) to get 199 from 0.
- 200 - 255: 1/2 * 1/128 (happiness/steps) = 1/256 (happiness/step), or 14336 steps (1181.86 seconds) to get to 255 from 200.
- Added together, 2110.47 + 1181.86 = 3292.33 seconds. (Note - this is approximated, assuming exactly half the time there is an increase in happiness. This is obviously not true in real life.)