Rounding Up Minutes above 8, 23, 38, 53 to the nearest quarter hour - excel

Question

Here’s a challenge for someone. I’m trying to round session times up to the nearest quarter hour (I report my total client hours for license credentialing)
8 minutes or above: round up to 15
23 minutes or above: round up to 30
38 minutes or above: round up to 45
53 minutes or above: round up to 60
Ex: in the first quarter hour, minutes below 8 will be their exact value: 1=1, 2=2, 3=3.
When 8 is entered, it is automatically rounded up to 15 (the same holds true for the rest of the hour: ex: 16=16, 17=17, 18=18, 19=19, 20=20, 21=21, 22=22. But 23 through 29 are all rounded up to 30.
Ideally, I could enter both hours and minutes in a single column, ex: 1.54
However, I realize that it may be necessary to create a separate column for hours and minutes in order to make this work (i.e., so that my formula is only concerned with rounding up minutes. I can add my hours and minutes together after the minutes are rounded.) Thus:
Column A = Hours (3 hours maximum)
Column B = Minutes
Column C = Minutes Rounded up to nearest ¼ hour
Column D = Col A + Col C
In column B I would like to enter minutes as 1 through 60 (no decimal- i.e., in General, not Time format)
38 minutes in column B would automatically be rounded up to 45 minutes in column C
Does anyone have any ideas? How can I do this using the fewest number of columns?
[A Previously posted question - "Round up to nearest quarter" - introduces the concept of Math.Ceiling. Is this something I should use? I couldn't wrap my head around the answer).
With Grateful Thanks,
~ Jay

Answer 1

How's this go?
DECLARE #time DATETIME = '2014-03-19T09:59:00'
SELECT CASE
WHEN DATEPART(mi, #time) BETWEEN 8 AND 15 THEN DATEADD(mi, 15-DATEPART(mi, #time), #time)
WHEN DATEPART(mi, #time) BETWEEN 23 AND 30 THEN DATEADD(mi, 30-DATEPART(mi, #time), #time)
WHEN DATEPART(mi, #time) BETWEEN 38 AND 45 THEN DATEADD(mi, 45-DATEPART(mi, #time), #time)
WHEN DATEPART(mi, #time) BETWEEN 53 AND 59 THEN DATEADD(mi, 60-DATEPART(mi, #time), #time)
ELSE #time
END

Answer 2

Assume "sessions" is your table (CTE below contains 2 sample records), with session start time & end time stored (as noted in comments above, just store these data points, don't store the calculated values). You might be able to do the rounding as below. (not sure if this is what you want, since it either rounds up or down... do you not want to round down?)
;WITH sessions AS (
SELECT CAST('20140317 12:00' AS DATETIME) AS session_start, CAST('20140317 12:38' AS DATETIME) AS session_end
UNION ALL
SELECT CAST('20140317 12:00' AS DATETIME), CAST('20140317 12:37:59' AS DATETIME) AS session_end
)
SELECT *, DATEDIFF(MINUTE, session_start, session_end) AS session_time
, ROUND(DATEDIFF(MINUTE, session_start, session_end)/15.0, 0) * 15.0 AS bill_time
FROM sessions;
EDIT:
Hi Jay, I don't think you mentioned it is an Excel problem! I was assuming SQL. As Stuart suggested in a comment above, it would be helpful if you modified your question to indicate it is for Excel, so that others can possibly get help from this dialog in the future.
With Excel, you can do it with two columns that contain the session start date and time (column A) and session end date and time (column B), plus two formulas:
Column C (Actual Minutes) = ROUND((B1-A1) * 1440,0)
Column D (Billing Minutes) = (FLOOR(C1/15, 1) * 15) + IF(MOD(C1,15) >= 8, 15, MOD(C1,15))
This is what my table looks like:
3/18/2014 12:00 3/18/2014 12:38 38 45
3/18/2014 14:00 3/18/2014 14:37 37 37