How long should I wait for a reference request response?

Basically I used to work in a specific field but left for about two years to explore other options and am now applying for a job back in that same field. I reached out to a prior supervisor from the old job to ask if they’d be ok with me listing them as a reference since they’re familiar with my work in that field.

How long should I wait for a response before assuming it’s a no or that Im being ghosted?

I’m far from being at the point to reasonably panic but I’m also just anxious by nature and in unfamiliar territory. Any experience or guidance is appreciated!