There is never time to make a proper training program, however, not having one, may lead to many errors of new employees. If you notice, that the errors can be avoided by having a training program, make one. And then adjust it on the go, as more training is needed.
To every new employee assign a person, who will be their mentor.
That’s a common practice in organizations.
When the mistakes of new employees become an issue for the company (for example, when they are slowing it down), prepare a training program in order to avoid them in the future.
You will never be able to avoid all mistakes, but you can prevent most of them in the future.
Adjust the training program on the go.
New mistakes of new employees will tell you what’s really needed in the training program.