How many times a day I should exercise using dumbbell?

Answer 1

Hopefully, you are using two, one in each hand, but how often depends upon your abilities and what you are trying to accomplish.
My weight lifting coach said once for weight lifting; once at one weight, put on more weight, lift once, and so on. Dumbbells are used in each hand, independently, to do what you can't do with weights, such as pushing your arms to the side, behind you, etc. The problem with weights and dumbbells is the possibity of tearing a muscle, which will hurt like every thing and put you behind. That is one reason why "slow and steady" works. If you are tiring, QUIT for the day.
Of course, if the dumbbells are below your ability, then more often and longer is safe.