date and time: referencing questions related futures market data organization

Hi I am a futures trader and have several hypotheses that I seek to prove or disprove using excel as my stats interpreter. I am not very good with excel but have figured out some basic formulas which allow me to do what I need to do very slowly and inefficiently. My current methods will never be practical and would take 3 life times of work to draw any meaningful conclusions.

The first and most important thing I need is some kind of macro for referencing date and time in all my formulas. Everything hinges on this, once I have that I will move onto the next thing:

For example:
I want to create the two following fields that automatically pull a the correct cell range for me:

Field 1: Start Date and time
2013/5/28 22:30
2: End date and time.
2013/5/28 22:40


So what I want to happen is that by typing in the date and time it will pull the range of cels for me and auto reference the correct range in my forumulas of interest.

FOR EXAMPLE: the dates and time entered into the hypothetical fields above turn up a range of A3:A13 but i want to SUM the corresponding rows in column K on that date range in this case k3:k13, and additionally have that range change in accordance with what I type into the date and time fields. How can I accomplish this?

Any help I get here will never be forgotten and would be happy to both share and explain how to interpret my findings to any willing helpers.