[SOLVED] Equations using time

[JukeBoxHero]

I have a problem where i have some set times. These times are described in local hours. i need to find the GMT equivalent, and the EST equivalent.

When i do a simple =F2+C2 it works and gives me the correct value.

1) When i subtract more then there is value, it ends up with "#######" ex. =H2-C2
2) I need the 24 hour clock to work, where it uses 24:00 as 12PM instead of 00:00 ex. =i3-E3
3) i will also need to take the GMT time and subtract 5 hours for EST. Apparently subtracting a # from time does not work. Most likely because its a difference in formatting, so i temporarily used a column with the time value i wanted to subtract.

Are any of these possible?

I have attached a sample Sheet so that you can see what i am working with, hope it helps.