According to the rules you can check in till 1 hr after the arrival of train at station. But as you know rules are not followed on IR. You can check in any time till the check out time. I aked this to the attender of retiring room at Mumbai central.(My check in time was 8 pm, so I asked in the morning itself whether I can check in after 8 pm) He said you can check in any time till your check out time.