What is the best time to conduct trainings - during work hours or after work hours?

programmed scheduled and the psychology we put in places speaks for the timing. For example, fitness programs is best for morning work hours. This is when the intensity of the whether is not very high. This blends with the chemistry of the body system no matter the vigorous nature. After work hours is better for strategic formulations and asides.

Best time is working hours and in working hours i always plan avoiding 1st and 5th working days of the week.

Well, Sunday and Thursday are typically the least effective days to hold important meeting/trainings. Many employees use their personal or vacation days to have an extended three-day weekend. Therefore, you may find that essential employees are not there every Sunday or Thursday. Also, employees are typically still in “weekend mode” on Sunday. On Thursday, they are likely to be rushing through the day in anticipation for two days off. Holidays on Sundays may also affect meeting availability.

Note: Working days and weekends are as per Dubai Government.

I find that giving training furing weekend or holiday is more fun, not just learning. 

during working hours even if its more cost but the sychology of employee will not accept to use time from his personal life for training , just special cases

I believe it works quite well during work hours too. We just need to make sure that it is the off-season time of the calendar year and the whole Section / Department is not attending together. This would make sure that usual work goes on as usual while learning also happens!

During working hours is best. Trainee gets some time from work and then he will be willing to concentrate more and would be happy to learn something new in working hours.

Weekends are good if employees can attend

This question does not make sense.  "After work hours" means time when you are not at work, but if you are in a training session then by definition you are at work. 

Training can disrupt the flow of routine work, and so it is often carried out outside usual work hours or at weekends.  Staff should obviously be paid for this time.  Whether training occurs in ordinary working time or outside depends entirely on circumstances.

In all cases, consult the staff before deciding.  Ignore their advice at your peril.

Many companies abuse their power by bullying staff into attending training sessions in the evenings or at weekends and not paying them.  This is unethical.

should be make balance

staff alawyes need it on work hours

co. need on weekends

so we can make deal between them 

Thanks for invitation.

I think working time is the best. Every body starts his day with very fresh mind and will be willing to accept the inputs easily.