Late check-outs are admittedly very inconsistent. If for example you are checking out on a saturday and the hotel is going to be full that saturday night, you are very unlikely to get a late check out because the hotel wants to get those rooms turned over ASAP. Along the same lines if you are checking out on a sunday and there are very few people checking in that night, you should have good luck. Here's a hint: when you call to ask for late check-out, first ask "is the hotel going to be very full tonight?" If they say no, you've got leverage. Its sneaky, but it works. As far as tipping for the late check-out, most of the time its cut and dry whether or not the agent can extend your check-out time, so you will probably be tipping for something you could have got for free anyways.
On the other hand, you should definitely tip the concierge if they have made arrangements for you. Some people prefer to wait until after they see if they like the suggested restaurant or show and then tip accordingly.