I concur with others. About 10-20 min of warm-up minimum and 10-15 min of cool-down minimum. What you do between matters somewhat on what you're trying to accomplish.
Are you preparing for a hilly race, then potentially tempo pace up and down the hill at set time duration? Like for example, for simplicity say it's 0.2 miles and your HM pace was a 9:20 min/mile. Depending on the grade of the hill would dictate how much off you would be on both the downhill and uphill and it isn't realistic to believe that is what you're going to do on race day as well. In general, uphill will cost you more time than you can make up on the downhill. But if you run it a few times and get a general idea from your Garmin (or Google Earth), then we can come up with a general sense. But for example's sake, let's say the combined effect of the uphill and downhill is a grade adjusted pace of +10 seconds. So flat HM Tempo of 9:20 = uphill and downhill of 0.4 miles at 9:30 pace. For HM Tempo, you could do intervals of 6 x 10 min, 4 x 15 min, 3 x 20 min, 2 x 30 min, 15+20+5+20+15 all with some rest breaks (maybe 1 min rest every 7.5 min run). Volume wise, I probably would limit it to 60-80 min of HM Tempo pace work at the very most. I typically try to stay under 60 min.
Now if you were aiming to just get in a hill workout that's for the purpose of building a different type of muscular endurance, you could do something like
@michigandergirl is talking about. For that, here's a seven week sequence:
1.5 mile WU + 2 sets of 5 x Uphill (30s w/ 1 min RI between each) w/ 5 min RI between sets + 1 mile CD
1.5 mile WU + 10 x Uphill (30s w/ 1 min RI between each) + 1.5 mile CD
1.5 mile WU + 5 x Uphill (60s w/ 2 min RI between each) + 1.5 mile CD
1.5 mile WU + 3 x Uphill (90s w/ 3 min RI between each) + 1.5 mile CD
1.5 mile WU + 5 x Uphill (30s w/ 1.5 min RI between each) + 1 mile CD
1.5 mile WU + 4 x Uphill Ladder (30s + 60s w/ Double rest min RI between each) + 1 mile CD
1.5 mile WU + 3 x Uphill Ladder (30s + 60s + 90s w/ Double rest min RI between each) + 1 mile CD
In this particular case the variable being manipulated is length of time running uphill and towards the end total volume of running uphill (starts off around 5 min and ends at around 9 min). The resting interval length (1 min per 30s) is mostly held constant, as is the pace of the run and rest. Like
@GreatLakes mentions, the workout is done when you can no longer maintain a steady/consistent pace for each interval. Form matters when running uphill and a loss of form means the workout isn't doing it's intended purpose anymore. For this person, this leads into other training later for the goal race.
Or a different person with a slightly different desire:
1.5 mile WU + 2 sets of 5 x Uphill (30s w/ 1 min RI between each) w/ 4 min RI between sets + 1 mile CD
1 mile WU + 2 sets of 5 x Uphill (60s w/ 2 min RI between each) w/ 4 min RI between sets + 1 mile CD
2 mile WU + 10 x Uphill (60s w/ 2 min RI between each) + 1 mile CD
1 mile WU + 5 x Uphill (30s w/ 1.5 min RI between each) + 1 mile CD
1.5 mile WU + 6 x Uphill (90s w/ 3 min RI between each) + 1.5 mile CD
1.5 mile WU + 8 x Uphill Ladder (30s + 60s w/ Double rest min RI between each) + 1 mile CD
1.5 mile WU + 4 x Uphill Ladder (30s + 60s + 90s w/ Double rest min RI between each) + 1 mile CD
1.5 mile WU + 20 x Uphill (30s w/ 1 min RI between each) + 1 mile CD
1.5 mile WU + 5 x Uphill Ladder (30s + 60s + 90s w/ Double rest min RI between each) + 1 mile CD
This one is heavier on the volume, so I expect the relative pace/effort will be slower than the first person. Same rules apply though, if consistency of intervals fades, then it's time to stop. For this person, this is the primary purpose of training with the goal race coming after.