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There is so specific amount. From what i heard from katha done by Giani Thakur Singh ji, he said a lot of mahapurukhs have done 101 japji sahib but again its a long shot. You should start with 5 japji sahib a day and work on you way up and if you start experiencing anand in doing paath and u can start living your life according to it, you will be on your way to God.
Thats all i know so i shared it with you.