Just making sure you understand the interface:

The first page you get when you enter your time is not your training paces -- it is your projected time in other distances. So if you enter 30 minutes for a 5K, it projects 1:02 for a 10K and 8:38 for a mile. These are the times you might achieve in an all-out race, provided you have trained for it.

If you click on "training paces" below race times, it gives you recommended paces for very specific workouts.

For example, for a 30-minute 5Ker, the default recommendation is a 10:54 to 11:43 pace for easy runs.

For a tempo run, your recommended pace is 9:50 to 10:08. A tempo run is a short, high-intensity run, usually around 20 minutes.

For a cruise interval, you are suggested to run 800 meters in 4:20 to 4:33 (this is total time, not time per mile! That's the equivalent of an 8:40 to 9:06 mile). Etc, etc.

Does this seem more reasonable now?

Try it. See how you do. If you need to adjust the pace, do so. If you think your last race was a fluke and aren't comfortable with those paces, feel free to use your previous PR and gradually increase it from there.

And if you put your previous PR (around 29:30?) for the first time and the 28:18 as the goal time, it will spit out different (slower) paces, so you could always try that too.

FWIW, I used the Runner's World calculator for my training paces which is similar but a little slower than McMillan. http://www.runnersworld.com/tools/training-paces-calculator

Not really...the training times it gives for my 5k PR 28:18 seem really fast to me. The easy pace is ok. The slow end of the long run pace seems ok, but the tempo is what scares me

Depending on the individual training plan, "tempo" run can have a lot of different meanings. McMillan defines a Tempo run as a 10-to 40-minute run. Given that you can run 28 minutes at a 9:06 pace, you shouldn't have a problem running 10 minutes at McMillan's recommended pace of 9:16 to 9:35. The effort for a tempo should be a little easier than when you are going all-out in a 5K, but these paces are slower than your 5K pace, and typically a tempo run is shorter in duration than what you take to run a 5K (I usually think of them as 20 minutes. If you want to do a longer tempo run, you could use McMillan's "steady state" times -- those are for runs ranging from 25 to 90 minutes).

The other possibility, given that you are skeptical about your 5K time, is that the course you ran on was a little short. For example, if the course was actually 3.05 miles rather than 3.1 (this is quite common!), then your "real" 5K time would be about 30 seconds longer, 28:49. This would put your tempo pace at 9:26-9:45. Does that seem more reasonable?

The other day I ran 4 miles at a 10 min pace, which was steady state per mcmillan and I was pushing and it was what I would consider a tempo. I guess I didn't really realize a tempo could be less than 2 miles so that is good know. I just always figured they were about 2-4 miles, even though I know some people do much longer ones. Good info!

I took the USATF certification course a couple years ago and was amazed to find that even 100-meter runners do tempos of around 60 meters or so! So when someone says they are doing a tempo, it pays to find out exactly what they are talking about!