As reviewed in Roediger, H. L., & Karpicke, J. D. (2006). The Power of Testing Memory: Basic Research and Implications for Educational Practice. Perspectives on Psychological Science, 1(3), 181–210, experiments which successfully demonstrate the testing effect usually use retention intervals of several days or longer. When tests are administered immediately, more studying may be better than more testing (see also Worked example effect).
Leahy, W., Hanham, J., & Sweller, J. (2015). High Element Interactivity Information During Problem Solving may Lead to Failure to Obtain the Testing Effect. Educational Psychology Review, 27(2), 291–304 in experiments 1 and 2, they find an inverted testing effect when testing is immediate