Colludium, Using the plugin to convert to a timestamp is pretty much the same idea as what RamPackWobble was suggesting because it returns a single integer, only it also incorporates the date (as well as seconds and milliseconds). Then you can subtract one timestamp from another one and calculate how many days, hours and minutes is between the two.
Or, if you want to add 4.75 hours to a timestamp you would have to convert 4.75 hours into milliseconds, Round(4.75 * 60 * 60 * 1000) = 17100000, then add that to your starting timestamp.
One thing to watch out for with the plugin is that date.day(timestamp) returns the day of week, not the day of month, use date.date(timestamp) to get the day of the month. This confused me at first, and obviously others if you read through the forum thread for the plugin.
so, if you set a global variable "CurrentTime" = date.UnixTimestamp
then ask it for date.day(CurrentTime) you would get 5 for Friday, while date.date(CurrentTime) would return 31 because today is the 31st of January.
The rest work the way you would expect (Year, Month, Hours, Minutes, Seconds).
To get a timestamp for a given date/time (for example 1:30 pm tomorrow) use: Date.Date2UnixTimestamp(2014,2,1,13,30,0,0)