"At the right time" vs "at a right time"

Tell me please what is the difference between the following sentences.

It is totally fine to add suplementary exercises to the main lifts. Just do it at the right time.

It is totally fine to add suplementary exercises to the main lifts. Just do it at a right time.

I heard the latter in a podcast where two native speakers discussed strength training. I was totally confused because I thought that only the definite article could be used before words like right, or wrong. If the second one is also right, then what shade of meaning does it bear?

It seems natural to always expect the rather than a before right time, because there often is only one right time for a particular thing. This, however, needn't always be so. Suppose that it is OK to do something either between 10 and 11 AM or between 2 and 3 PM, but that it would be wrong to do it at any other time of the day. Suppose, moreover that it needs to be done only once, and that it makes no difference whether it is done during the 10-11 or 2-3 timeslot; neither is better than the other. In that case, it would seem perfectly appropriate to instruct somebody to do it at 'a right time'. In fact, in such a scenario, telling someone to do it at 'the right time' could be confusing, because it would make the person wonder whether there are some considerations that make one time better than the other, after all.