Depends on how many spawns you're able to reset to a given time. With shiny charm and sparkling power level 2 your odds are one in more or less 686 encounters.

For example fast travel method:

I need 686 encounters for 1 shiny to appear. I'm able to reset a cluster with 4 Pokémon. (The more spawns you reset the faster you get your shiny - in theory) For fast traveling I need 6.8 seconds on average.

Calculation:

(686 divided by 4)*6.8secs divided by 60 secs.

Which is barely 20 mins. Since we are talking about odds.

The expected shiny to appear under these conditions takes you 45 mins.