There are a lots of ways to stretch out the hip joint. Butterfly is a great one but there are others. For example try to gently pull your foot behind your head. You should feel it stretching differently that butterfly does. It's going to pull on your outer glut, instead of the inside of your thigh. That tells you that there are other muscles and tendons involved here. Here are some other ideas for you based on stuff I use:
When doing butterfly:
1. you can press down on your knees to open the stretch (this is probably what you're doing already in butterfly)
2. bounce your knees up and down
3. lean forward pressing your head down toward the mat.
Eventually your goal is to get your butterfly flat on the mat but also get your head to touch the mat. The ultimate goal is to get your butterfly flat, your head on the mat, without feeling any tension or resistance so that you can comfortably sit there for an extended period of time without discomfort.
Lotus:
1. stretch using the lotus position itself
2. stretch single lotus, each side.
3. if you can do double lotus, do it.. but if you have any pain or pressure in your knees at all, go back to singles. Do NOT force double lotus
4. once you have double lotus, start moving your head to the mat
Same ultimate goal here... double lotus, head on the mat, no tension or discomfort.
Foot to chest:
1. take one foot and pull it toward your chest with the opposite hand. If you feel pressure in your knee you can support your knee with your same-side hand (or by wrapping your arm around your knee in New York style).
2. while supporting your knee, keep turning your leg in, trying to get your foot to touch your chest (make sure to support the knee, you want this opening your hip not putting pressure on the knee)
3. Once your foot can touch your chest, take your same side arm and hook it over your knee (like the opposite of a new york.. your upper shin is in your armpit
4. pull your leg as tight to your chest as you can
Ultimate goal here is to get your entire leg flat against your chest and parallel to your shoulders without discomfort
Foot to chest with push and raise
1. using the same position as foot to chest with your foot and knee as close to your body as possible, push on the sole of your foot while turning your core away from that leg. You should really feel a good stretch in the inside of your hip this way.
2. grab your heel with both hands and raise your foot in the air. You should feel the stretch move from your inner hip into your glut. Make sure you dont get pressure in your knee.
3. lower your foot to that it's head height and try to get the sole of your foot to touch your ear. Same as always, no pressure in the knee.
Other stuff that will help:
1 sit with one foot touching your balls and the other one out straight. Lower head to outstretched knee. Mainly works the hamstring
2. do the side splits (I'm sure you know what this is). YOu'll feel that in your inner thighs, but differently than a butterfly which works the inside of your hips, not your thighs.
3. front splits, both directions. This one is really hard and can take years.
As far as how often you do this, probably more than you are. I do this all the time. If I'm sitting in a chair I often pull my legs up into my lap and stretch my hips. Old habit from years of TKD. I see Eddie doing this also. He always seems to be stretching out his hips.
If you're watching TV, get off the couch and onto the floor and stretch. Just sit in butterfly and bounce your knees if you want.
As far as your timetable, I would be a little more conservative than that. I've watched guys go from very low flexibility to very high but it often takes years to develop. Be patient and keep at it.
You should push your flexibility but not too much! Last thing you want is to strain the tendons. You are literally lengthening them when you do this. It takes them time to adjust, so dont push too hard. Best to be consistent and stretch regularly instead of less often but pushing too hard.
And remember to always protect your knees when stretching your hips out.
Good luck!