The best time is now

If you have a member of the team who is behaving or performing poorly and you have treated them with empathy and given them every opportunity, then action needs to be taken.

Waiting will not only prolong the agony, but it will continue to undermine the safety within your culture forcing good people to leave and seek better conditions elsewhere.

Having managed this process myself a number of times I know how hard it can be. However, the best time to address these issues will always be now.