First of all the standard cannot be applied to all concerts & all artists. It will vary according to the total time of the concert, the singer's ability & the proficiency of the mridangist.
The mridangist who can impress upon, attract & create an impact on the audience with his genuine, tradition-based novel ideas with pleasing vibrations, rightly deserves a reasonable duration to present his expertise to the audience.
The singer must be a person who can understand & enjoy the performance. He should delegently put the Thala for the Thani. The audience will also be automatically drawn in to the enthusiasm. To make it possible, the mridangist must be s very capable person who can sense the pulse of the singer, his weakness & the mood of the audience. In such a situation a full 30 to 40 minutes of Thani will not be boring but enjoyable.
But in the present day situation those having not enough high standard but can manage with a well tuned instrument & be accommodative to the fancies of the vocalists are preferred more. What can we expect of these substandard performers? But they have their own reasons. They feel that if they do not confine to the limits imposed by the center performer & give vent to their knoledge taking reasonable time, they may not be engaged for future concerts.