About six months ago I had a Dell Optiplex motherboard fail and they attempted to schedule a tech to come out the following day. I was not available for that and scheduled it a few days later but they did make as full of an effort as can be reasonably expected to make it happen within one business day.

The default warranty on at least the Optiplex line is one year of next business day service and upgrading to three years is cheap. I've never had a situation where same day service was worth the extra cost but it is an option.