How long should I wait to use a power trained player after power train?

[Teda]

Just bought a fast trainer and trained him close to 7 stars, how long do you guys think I should put him on bench before include him in starting line up?

I am crazy about this season, a disaster to me, so have to buy this fast trainer and power train him. But I don't want to rush to use him as I heard about some past experiences that it would be better to wait for a couple of days.