Hi Zuni,
I would definitely keep it closed. So many problems can be created by interfering too soon. It is really hard to hold back but it is normal for them to pip and then rest a while. I would do your best to relax and just think about what will most likely happen tomorrow. I know I have learned the hard way by messing with them too soon. They can bleed out, and sometimes, even if they don't bleed, they still die from coming out too soon. If you think it is hard to wait, it is even worse to know that if you had only waited a bit longer you would have a chick. Some chicks pip and pop right out while other take their sweet 'ole time. The only time I help is if I see the chick trying to unzip and it's not making it through the membrane, or if it keeps making the pip hole bigger and bigger but can't seem to turn. I'm actually going through the same thing right now. Today was day 18 and I just unplugged my turner!
Richard