For the first question, answer is no, TDS on salary is required to be deducted while making payment of salary to employees be it during the month or in between the month or quarter. And the same is to be deposited upto 7th of the following month except for the month of march by 30th April of the next year.
For the second question, there is no such provision deducting TDS only on crossing certain limit during the year, instead, the employer has to estimate the salary payable during the year to every employee and if it crosses the basic exemption limit then he should deduct tax on an average rate applicable to particular employee from the very beginning of the financial year on making payment.