Are you talking about how long do they post with your airline? American and Alaska put through weekly batches so at most you should see those restaurants visits show up as actual miles within two weeks of dining.
Delta is still under the old monthly batching so Skymiles only credit the first week of every month - a pain if there are meals late in a month that need to be given retroactive credit manually by Idine!

If you are concerned about posting, you should check your actual iDine account (as opposed to your airline) 4 or 5 five calendar (not business) days after the meal. I'm a fairly regular iDiner and only a couple of times has a meal come through later than the 5th day after dining. If hasn't been credited to iDine a week or so after your visit, give them a call. They'll either tell you why it might have been rejected.
Example: you dined on a Thursday, the restaurant puts through all meals the following business day, and they just happen to have a Friday blackout. Idine would instruct you to send in the receipt dated Thursday so they can reverse the denial they have on record. (Time Cafe on UWS of Manhattan had this problem more than once - management seemed not care even though it meant that blacked out Saturdays would go through as valid)
Usually, it is the case that the meal has fallen through the billing cracks somehow - iDine has no record of it whatsoever and the rep requests you send them the receipt. Credit for those typically appears in your online iDine profile a week or so after they receive your paerwork. Note: those visits are listed under the date you dined not the date they post it as "Manual Tickets". You might have to scroll back to check on it if you've had visits since then.

Good luck - it's a great FREE program with only minor glitches so far I've found.