There are standard SMARTnet (SNT) offerings from Cisco that are the norm including 24x7x4 and 8x5xNBD support offerings. These are probably two of the most popular offerings, but there are many others out there as well.
It is important to note that each of the SMARTnet offerings from Cisco include 24x7x365 access to the Cisco Technical Assistance Center (TAC). I am not here to promote TAC by any means even though it is a world class organization, but this is questioned by the “8”x”5”xNBD usually found in the description of the SNT SKU being sold. The 24x7x4 and 8x5xNBD most importantly are referring to the turnaround time to get hardware replacements. So what if you’re an organization that has 200 user access layer switches, and you already spare a bunch of additional switches? Good question, and for me personally, I would first move away from 24x7x4 SNT if that was the case. Since the concern is no longer hardware replacement, the most important piece to the DAY 2 support puzzle becomes having a number to call in the case of a problem. Again, this is a where TAC comes in and you can leverage 8x5xNBD on the switches. It would be ideal to do a ROI of sparing vs. different levels of SNT being chosen to see which makes the best financial sense for the organization. Cisco or your local partner can help you with this.