Is there any time limit for issue of notice under section 76 in cases where tax collected but not paid to Government

No. Notice can be issued on detection of such cases without any time limit. Once show cause notice is issued, the proper officer shall pass the order within 1 year from the date of issue of such notice.

(ICAI FAQ PUBLICATIONS 06-09-2017 Tax collected but not paid to Government: FAQ NO. 34)