How much time a cup of tea or cup of coffee to take effect on brain ?

Varies: If you are just talking about caffeine, maybe 10-20 minutes, however for regular coffee drinkers the effect can seem instantaneous - this is due to mechanisms of Dopamine release in anticipation and satisfaction of a reward (e.g. A nice cup of joe) that activates the brain. Duration of the caffeine effect varies - few hrs to, >12 for about 10% of the population are slow metabolizers of caffeine.