it depends on the TLD, is it .com/.net? if so, if its in pendingdelete now it will drop within the next 5 days or less.
an easy way to check these is to put them into snapnames or pool and those service will generally tell you when the domain is dropping assuming that it's in pendingdelete status.
if its in say, registrar-hold or redemptionperiod the wait is usually much longer, and the domain can be renewed at any time. generally, the wait for those domains is about 80 days.
if i remember correctly:
registrar-hold lasts 45 days
redemptionperod lasts 30 days
pendingdelete lasts 5 days
above figures are only for .COM./NET other TLDs have very different rules.