Do you believe that the most suitable timing for training courses are during the working hours / after working hours or during the week ends ? why ?

the best time for training is during working hours because for trainee training after working hours will be useless because all of them want to leave and go home training while week end days is not as good as training during working hours because it's simply a week end and the trainee own that time for himself 

Training is divided mainly into two parts

 On the job training and

Off the job training.  

Expectation from any training is increase employee efficiency, productivity and many small and long term goals.

So any training should have employee involvement and engagement to rip of the benefits.

On the job training has no other option but to be done on working days....

Off the job training should be planned on last working day of the week along with weekends with some type of recreation activity for keeping employees engaged. Weekly off day should avoided until and unless it’s very urgent and necessity.

Thank you for the invitation

Training programs timing & place depends on the type of flaw or gap to be bridged

During the working hours, definitely. First, because each employee values his spare time and does not want to spend it working. Second, after 8 hours of working (or after 5 working days), it is just difficult to concentrate on the training. The training is not just an act of presence, the trainee should really learn, so all his attention should be focused on the training.