For a 5k a proper taper (reduced training allowing for recovery) going down from your intensive training period will take about 2 weeks, possibly longer. This will probably combine 2 days prior to the event doing virtually no exercise.
This is often one reason why after a week of illness you can come back quickly to do a PB. Your body has had a chance to recover from your over-training !
If you do 5k runs frequently, for example with www.parkrun.com, then it becomes difficult to properly recover. You just can’t train Monday to Friday and then expect to do a PB on saturday and recover on Sunday.
You will effectively be limited to an ‘optimum’ (hmmm?) training period of Monday and Tuesday, perhaps Wednesday if you are a youngster! That’s just not enough to progress to a high level. So you can’t race to your optimum every week.
So I would suggest watching weather reports carefully. If it’s going to be a hot windy day on Saturday then boost up the training in the days immediately preceeding the race as you aren’t going to do a PB anyway. Do at least a 2 day taper and watch your diet when the weather looks right.