In Construction of PCC Road and street, In the first step lean concrete (1:4:8) is laid and then 4" thick 1:2:4 is laid, the question is after how much duration 1:2:4 be laid on 1:4:8.?

Dear Faisal what will be the disadvantages if 1:2:4 is laid after one or two hours of laying 1"4:8

it depend upon the atmospheric tempurature also but in general minimum 24 hours maximum 72 hours.