I need a set of running workouts that meet my criteria below.?!

I need a set of running workouts that meet my criteria below.?

This is for long distance cross country running...

First, i have about 30-50 minutes to do this workout...shorter workouts are best schedule-wise. I cant hit hills so forget those. I have 1 month. I need it as effective as possible, and its for endurance not speed. I need a really good base before my fall season begins. I'm in decent shape. I run 5 miles in 40 minutes currently. In terms of just a workout I don't want to go much faster than that. But 2 miles i'll do in 14 minutesish and 1 mile in 6 minutes. These are not race pace though so if you want me to go fast as race pace just say so. Feel free to include ab workouts and strenght training but keep in mind I dont have a gym and other stuff, so i need stuff i can do anywhere. K tks a lot.

My suggestion to increase endurance would be circuit training and you can do it anywhere. I played basketball and soccer among other sports that you need endurance for. I usually did this in a gym but it can totally be done outside. You just need to determine how far you wanna run between each circuit. I'm not sure what the total distance is like for cross country running but you can adjust this a little more to your needs. For example of circuit training it would go like this....
1) Run 1/4 mile
2) Drop and do 50 push ups
3)Run 1/4 mile
4) Drop and do 50 crunches
5)Run 1/4 mile
6) Drop and do 50 jumping jacks
7) Run 1/4 mile
8)Drop and do 50 mountain climbers

You continue in this manner for as long as your time allows. But the most important part of the whole thing is that you never stop. You never take a break. You keep pushing and you need to keep your heart rate elevated the whole entire time. You can substitute the distance and different exercises. Whatever works best for you and your specific needs. But the general format is one of the best ways to increase your overall endurance. Best of luck! Hope it helps :)