If you are going to come all the way out of the cylinder, then I think you should pump for at least 10 minute cycles instead of 5 and perhaps even go to 12-15 minute cycles. You could do three 10 minute cycles or 2 15 minute cycles. In the future, every once in a while throw in a four 10 minutes cycle session or three 15 minute cycle session.
Yes, you can use the 4hg pressure. I just mentioned I used the 3hg max on my “rest” days and if I go for a longer time, I get a similar of not better result.
Of course pressure is important to this, but the more I do it, I think the key to permanent growth and great results is longer pump times at lower pressures. So if you pump and only worry about pressure, you are missing the key ingredient which is time at size with no trauma or lymph build up.
You really must seriously consider buying yourself a 2” professional thick walled cylinder for you Christmas present this year. Pumping with the right size quality equipment will make a big difference for you I think.