[SalesForce] difference between two date time fields in days

Use the LEFT, RIGHT and FIND functions to grab the hours and minutes. Use the VALUE function to convert the strings to numbers. Multiply hours by 60 and add to minutes.

So 9.30 becomes 540 + 30 = 570

If PM convert to 24 hour equivalent (I.e add 12 to hours) 6.15 = 18 x 60 + 15 = 1095

Then subtract to get the difference and divide by 60

1095-570= 525 / 60 = 8.75

Here is what i did, I created a formula field "DateNow__c". In this formula field keep this as datetime field. In order to get EST or CST time zones here you have to find out the time differences in terms of hours. For example, EST time difference would be 4 hours , so i simply made DateNow__c as "NOW()-0.1667" where 0.1667 = 4/24 Similarly for CST, DateNow__c as "NOW()-0.2083" where 0.2083 is 5/24. From this timings i get my local time zones value,

Why i did this is because When i used something like this "TEXT((NOW()-0.2083) - LastModifiedDate)" did not give me the desired output.

Step 2: Now to determine the diff in hours and minutes. Normally difference will give some decimal values like 5.52 where 5 is the no. of days , 0.5 in terms of hours and 0.02 in terms of minutes. The below formula will give me the difference in hours and minutes. For example, Date A is 9/22/2014 5:40 AM and Date B is 9/22/2014 8:00 AM My result will be : 2.20 where 2 is the hours and .20 is the minutes. For example, Date A is 9/21/2014 5:40 AM and Date B is 9/22/2014 8:00 AM My result will be : 26.20 where 26 is the hours and .20 is the minutes. (even day wil be converted to hours)

(FLOOR(( DateNow__c - SomeDatetime__c)*24)) 
+
ROUND((((
((DateNow__c - SomeDatetime__c)*24)-
FLOOR((DateNow__c - SomeDatetime__c)*24))
*60)/100),2)

here FLOOR(..) - will give me the hours. ROUND(..,2) will give me the minutes in 2 decimal places. Hope this will do good to you in some way.