How often should I visit my Godchild? Do I have to be involved in everything?

So I was asked by a second cousin to be a Godmother to her child when I was in college. I was not close with the mother so I was confused to begin with why she chose me, but I felt obligated to say yes to being the Godmother (which now, I know, I should have politely declined...but that's retrospect). So I saw the Godchild during a Holiday, then only once at the first birthday part and nothing since then (it's almost been a year since). The thing is they tried making a time to visit with the child but both our schedules didn't mesh and I'm busy most of the time and it's difficult. Is it ok to only visit on holidays and birthdays? Or is that wrong? I know I'm being partly selfish by trying to do as little as possible, but when I grew up, I didn't even know who my godparents were and I met them like once or twice and I think I got a card on my birthday, but that's it. What is proper?