"Optimum time" refers to the most favorable or ideal period or moment for doing something. It is the point in time that produces the best results or outcomes. Full definition
They might take a week or two, working with optimum times for daylight and artificial sources to capture photos worthy of hanging on a wall in a gallery. (remonline.com)
But you can still get the most out of your organic posts by sharing them at optimum times, which tend to vary by platform. (entrepreneur.com)