Help? I am at the end of my first hatch. It has gone well for a first try with a 75% hatch.

I have a problem with one of the chicks.  It is stuck to it's shell by the umbilical cord and is getting weak.  It pipped yesterday morning and I had to help it free from the membrane.  I will try to give it some electrolyte solution and see if it perks up.  When should I consider cutting the umbilical cord?  The other chicks hatched 48 hours ago.  This one has come late and it is having problems.  Is there anything else I can do?