Epoxy is fun stuff! I had this happening to. Thought mine was incorectly labeled as Tower\Greatplanes had a recall but then I mixed up some more and it seemed about 30. On some epoxies I think the 30 is the time that is setup by. Not the working time. I got some epoxy at home depot and it said 25-30 on it. It was starting to setup in half that time. I think ambient temperature has an effect on it. You need to mix it more than 10 seconds. It needs to be thorough. Could be you're getting more hardener than resin to. Since you know how that epox sets up you can plan when you use it. Try a different brand and it will probably set up different.