You seem to have no problem if you can go on for 3-4 hours. Most people with ED either cant get it up at all, take a long time to get it up, or lose an erection too soon.
I remember I had particular problems the first time myself (using a Fleshlight - which can simulate a vagina) where althrough I was able to get an erection, I wasn't able to sustain it once it was inserted. (Other times when I was in the mood and did a fictional doggie-style it worked out really well). I've also done a probe with on enotalone and other guys reported losing their erection shortly after penetration with women. In fact, it could turn a woman off when that happens in some cases. I can forward that link if you are interested (too lazy to do that now).
Since you are using your hands, there is no way to know how it would be if you are putting it into a canal type opening, but since you are not masturbating on a limp erection or doesn't appear you are cumming too fast, it's looking good for you. Are you a teenager or something?