How do you keep the balance between your family and taking care of someone who is very sick?

I have a schedule that I try to stick to when it comes to visiting my mom, that allows me a little time to try to keep up on my life and family....well yesterday is one of my days to be with her. My husband's aunt and cousins threw me a surprise birthday party so I didn't get to the nursing home to see mom until after 6:30. Needless to say, I had 9 missed calls on my phone (I accidently walked off and left it on the kitchen counter) and one very miffed mom when we got there. She asked me if I would come tonight because I got there so late last night and I said sure. husband's car is stuck in our garage because of a huge snow drift he hasn't fully dealt with yet, so we've been car pooling to and from work. So, he's got a light day and will probably get off of work early so now he is throwing a fit because I told my mom I would come and see her tonight.

It's so frustrating, I don't know how to keep the balance between it all!