Part of your problem is that you are thinking in flat-file format, which means "Excel-like" for all practical purposes. That is why you are asking about a humongous table.
I might do something like this (and beware, I'm shooting from the hip.)
1. A table of calls, with among other things, the time logged and a link to the applicable agreement - BUT... the link to the applicable agreement might be through the name of the customer in another table and the actual link to the SLA category might be in the customer's entry in that second table. (I would do it that way.)
2. So... the call has the foreign key of the customer, which suggests a drop-down on the form you use and the drop-down is based on your customer list.
3. When you enter the customer, you select one of the possible SLA formats. Note that the SLA number doesn't have to be the SLA format. You COULD have another table of SLAs that lists the customer FK number and has the SLA as the prime key, but instead of having the details in the SLA, it sounds like you have a limited number of attributes. You can have another table of SLA response formats that include:
a. Service days - either Mon-Fri or Mon-Sun
b. Start of service per day - Either 00:00 ( midnight) or 08:00 or 09:00 etc.
c. Duration of service per day - either 24 or 16 (for the 08:00-20:00 case) or 10 (for the 09:00 - 17:00 case), etc.
d. Guaranteed response time - 4, 8, 16. Saying "next business day" is redundant because the answer is ALWAYS going to be "next business day." What varies is the start of the next business day, not the fact of response being on the next business day.
Now write a VBA function for which you give it the date/time of the call and four items I just described to you. From there, you can write code that says "compute the response limit based on the call start" and return a date/time.
Questions you have to answer (and will have to implement in the function) are:
Is it the 24/7 case? Then add the max response to the call time and that is your latest possible arrival time to be within the SLA
Is it one of the other cases? Then add the max response to the call time and see if that exceeds the (computed) latest response allowed under the SLA. I.e. if the SLA says 09:00 to 17:00 and you get a call at 12:00, a response limit of 4 hours is still today but a response limit of 8 hours is next business day.
Something you need to address is whether you automatically put calls at the start of the next business day or whether you can do some lag time. I.e. if the call comes in at 16:00 on a 4-hour SLA for 09:00 to 17:00, does the SLA say you must respond by 09:00 (start of next business day) or at 12:00 (1 hour from the day of the call plus 3 hours left over.)
The last thing you have to consider in the subroutine is whether the projected "next business day" is tomorrow or Monday (because the call came in late Friday on an SLA that was not 24/7). But that is easy enough because there are functions in VBA that can return the day of the week as a number from 0 to 6 or if you use FormatDateTime, you can return the name of the day of the week and do your tests on that.
The result of all of this computation goes back into the call ticket as the "computed latest response under SLA." NOTE: This might appear to violate a popular guideline often offered regarding storing a computation - but given that the customer might renegotiate a different SLA next year, it might be easier to just remember the latest condoned response, particularly if you were planning to do "efficiency" stats by comparing arrival time to latest allowed arrival time later.
The secret to doing this is to remember the advice of old Julius... divide and conquer. Break up the problem into pieces-parts and attack them separately.
