It sounds like you are interested in the Spacing Effect.
A search on Google Scholar for "spacing effect" for articles published since the year 2000 yields over 2500 articles some of which might be worth pursuing.
Perhaps you might want to start by having a read through the meta-analysis in Psychological Bulletin by Cepeda et al (2006). To quote the abstract:
The authors performed a meta-analysis of the distributed practice
effect to illuminate the effects of temporal variables that have been
neglected in previous reviews. This review found 839 assessments of
distributed practice in 317 experiments located in 184 articles.
Effects of spacing (consecutive massed presentations vs. spaced
learning episodes) and lag (less spaced vs. more spaced learning
episodes) were examined, as were expanding interstudy interval (ISI)
effects. Analyses suggest that ISI and retention interval operate
jointly to affect final-test retention; specifically, the ISI
producing maximal retention increased as retention interval increased.
You may also want to read Pavlik and Anderson (2008). They used a computational model of known spacing and practice effects in order to try to develop an optimal practice schedule for maximising learning and retention.
- Cepeda, N.J. and Pashler, H. and Vul, E. and Wixted, J.T. and Rohrer, D. (2006). Distributed practice in verbal recall tasks: A review and quantitative synthesis. Psychological bulletin, 132, 354. PDF
- Pavlik, P. I and Anderson, J. R. (2008). Using a model to compute the optimal schedule of practice. Journal of Experimental Psychology: Applied, 14, 101. PDF