New references to look at:

• Yoshida, Mariko; Iizuka, Tetsuya; Shiohara, Hisako; Ishiguro, Masanori: Mining sequential patterns including time intervals, Proc. SPIE Vol. 4057, p. 213-220, Data Mining and Knowledge Discovery: Theory, Tools, and Technology II, Belur V. Dasarathy; 04/2000
  
  
• C. Giannella, J. Han, E. Robertson, C. Liu, "Mining Frequent Itemsets Over Arbitrary Time Intervals in Data Streams". Technical Report 587, Computer Science Department, Indiana University, Nov 2003 www.cs.indiana.edu/ftp/techreports/index.html. An older version: C. Giannella, J. Han, J. Pei, X. Yan and P.S. Yu, Mining Frequent Patterns in Data Streams at Multiple Time Granularities (pdf), H. Kargupta, A. Joshi, K. Sivakumar, and Y. Yesha (eds.), Data Mining: Next Generation Challenges and Future Directions, AAAI/MIT Press, 2003.
  
  
• Oates for event-based sequence mining
  
  
• Parthasarathy on incremental techniques