Most of the SRS programs out there will handle the timing of your reviews. In the case of Anki, it’s really good about keeping them there for you, even if you miss your review date for kanji/sentence/whatever. However, if you’ve entered the cards ahead of time (or used something such as the Lazy Kanji Mod), new cards generally will be held back. To clarify, if you’ve told it to add 25 new cards/day, and one day you review 5, then only 5 are added the next day (for the total of 25 new).
This is fine from the standpoint of not getting stockpiled, but terrible in the sense that you aren’t progressing with new cards. Enough about the new, though, let’s discuss reviewing the old.
Each time you review, a “next review date” of some sort is set on that card (depending on the score you gave it). If you miss that date (for example sake, let’s say that date was June 3rd), then cards due on the 4th are combined into those due on the third. If you then review all of them, then both sets of cards will be due at the same time in the future (assuming the same review score was applied to each), making a larger review batch instead of having them spread out.
Human nature is to avoid large tasks (something I’ll be writing about soon) and focusing on small ones. If you let it slip to the point of having over 300 cards to review in a day, you’re more likely to slip further than if you had, say 50. Missing reviews causes a snowball effect that just gets worse, promoting even more procrastination.
So cut that crap out, and review your cards already! On time!
Oh, and one more thing – time-boxing helps a TON with this.