|First, what does your data look like?|
Are the Dates & Times in one cell, or are they separated into two cells?
Please post a short example of you data, AFTER reading this HOW-TO
which explains the use of the < PRE > tags for posting data.
From you post, do I understand correctly, that you need only Days & Hours?
What functions do you wish to preform on the data besides means, modes, standard deviation?
Also, be aware that Excel stores Dates and Times as
a number representing the number of days since January 0, 1900
plus a fractional portion of a 24 hour day: ddddd.tttttt.
This may impact the result of your analysis.