ok, i'm a newbie -- but persistent, willing to learn, and usually good at following instructions...

i don't know exactly how to get started with coding this... so i have nothing thus far... looking for beginning ideas.

goal: create a swimming pool party rental calculator for my neighborhood pool
inputs: party begin date and time, party end date and time, # of party people
calculation (this is my biggest hurdle): how to calculate the number of hours during "normal operational hours" and the number of hours "after operational hours". (reason: the cost per hour of the party goes up significantly for an "after hours" pool party)

example:
input party start time: 5/1/2006 6pm
input party end time: 5/2/2006 1am
number in party: 120

somehow? embed information about normal operational hours:
5/1/2006 9am-8pm
5/2/2006 10am-7pm
...and all other normal operational dates and times

Based upon the inputs, needs to return the following:
number of hours during normal operational hours = 2
number of hours after normal operational hours = 5

additional calculations are also necessary, but i think i know how to do those...

any help is most appreciated!!