Out of curiosity I tried out if the problem with date/time was also present with other data sources.
CSV Reader: OK because it interprets Date and Time columns as strings, and the type conversion node works OK as far as I could see. (attached CSV was used)
XLS Reader: NOT OK. See attached XLS (also for all Column/Cell references below).
Columns A and B are interpreted as strings (in principle OK)
Columns C - F NOT OK: these are conversions to parts of date or time values from Cols A and B using formulae.
Column G: Not OK. This is a conversion of Col B to TIME type. This is also a formula. This Column is interpreted as of type string and the values are corrupted completely on import.
Interesting is that the XLS Reader node understood the number conversion which I included in the XLS.
The attached XLS was created using LibreOffice 3.6 so it would probably be OK if somebody who has a "real" Excel could confirm my results.
This is KNIME 2.7.4 on Linux FC18 64-bit using Java SE Runtime Environment (1.7.0_21-b11)