I'm new in pond feeding. Help me with some ideas. There's about 10 koi in my pond.

Welcome Caitlin, the normal rule I go by is... As much as they will eat in about 15 minutes. You can feed up to 3 times a day. I'm no pro just hearsay.

I thought it was once per day, and not more amount-wise than they can eat in a span of 5 minutes. Not an expert on koi fish either, just what I generally found online.

Feeding depends on a few factors;
1) Filtration system
2) Pump
3) Time of the year (temperature)

If you have a great filtration system that has mechanical, biological, and chemical filtration then all things being equal you could feed your koi more than a system that has a lesser filtration system.

If your water pump can turn the pond over once every one to two hours then in theory you can feed your koi more because the water is being forced through the filtration system regularly.

In the Winter or when water temperature drops below and stays below 55 degrees for 10 or more days stop feeding your koi because they cannot digest the food (no stomach, just digestive tract) and so you waste the food and potentially make your koi sick.

So in summary, the better your filtration system and the better your pump the more you can feed your koi. I would feed twice a day or three times a day in warmer temperatures. Morning and later afternoon. Just as much as they can eat in a couple of minutes. Often, though, koi are pigs so you have to know when to stop feeding them.