How many/big are the koi and how big are the holding bins?
Properly sized and filtered you can do it long enough to rebuild a pond.
Using water from the pond and any filter media from the pond as well, would even throw in small river cobble or stone from the pond in the holding tanks, as well, these have a biofilm on them with an established bacteria population. This is to try and minimize any spike in ammonia from setting up the holding tanks, get plenty of prime/stress coat to help neutralize any ammonia that shows up in the water.
get a test kit also and do not feed them .I kept mine in stock tanks for almost a month .I tried not to stress them out as much as possible .Air pump and quilt batting in a temporary filter will help also
The fish can survive as long as they've got good enough water quality to avoid getting sick. This will depend on the size of your tank, the size and number of fish, whether or not the pond filtration media has been moved to the tank, and other factors like how often you feed the fish.
Prioritize keeping any biological filtration media from the pond alive, preferably by attaching it to the tank. This will spare you from having to cycle the cleaned pond, which could greatly slow down the rate you can return your fish to the pond.
If you're not able to use biological media from the pond on the stock tanks, test the water two or three times a day for the first day or so and determine the rate the ammonia builds up. You'll likely find that you need to do two or three water changes a day. These are messy fish! If you can, match temperatures when doing the water changes. Extreme temperature changes are not something you want to stack on top of fish that will be exposed to ammonia.
Good luck on your project! Sounds like a lot of work, but a great opportunity to incorporate new things or make the pond better!