Two sources that discuss the "Curve of Forgetting" and "Massed Study--Spaced Reviews" are Powerreading--Study Skills by Smith, Blake and Pryce (who cite Stanton) and How to Study by Thomas F. Stanton.  Stanton claimed that you can retain information longer through spaced reviews and the first review should be within 24 hours after material is presented.  (The best, most beneficial review is completed at the end of class.)  Stanton found that the greatest loss of information occcured within one day.

Elaine Wright wrote:

Yes. I'm thinking it is in  Walter Pauk's How to Study in College---
notetaking chapter, I think, --but it could be under the memory
chapter---says that if you don't "process" your lecture notes within
48 hours, your memory of that information decreases rapidly to
zero. How students "process" will vary.  Some read it over
(outloud), some keyboard their notes, some meet to discuss notes
with others, etc. The point is that you need to "pay as you go"---
study in short bursts bursts to transfer from short term memory to
long term memory.  Hope this helps.  I mention this in my study
skills workshops all the time because many entering students do
not look at their lecture notes until they see a test coming----and
that often causes memory overload.
Elaine Wright, Director
Dept.of Learning Assistance
Division of Academic Support
University of Southern Maine
Portland, Maine 04104
Portland, ME  (207) 780-4691