I don't think it is absolutely necessary to have a well-defined, or traditional, notion of God, in order to do Step Eleven. I say this because my first sponsor was an atheist. She was more devout about atheism, than I was in my deity-based faith, yet she never imposed her notions of her Higher Power on me. From her, I intuited that Love was our mutual Higher Power.
She believed there was no Deity and I was not sure. So I set out to discover and actually I could not wait until Step Eleven to find out.
Through a gratitude practice, I found my way out of a deep hole, which restored the faith I needed, in order to do step Four at all.
Even today, when I am re-set by a relapse, I return to this prayer of gratitude to reclaim my spiritual life, and restart my recovery.
For me the prayer part of step eleven is about being grateful for another day of life...and grateful for the opportunity to learn greater love and compassion from my challenges. Meditation is about becoming more present to the Love already with in me. I can do either of these anytime. Often for me Step Eleven comes naturally to me as I fall asleep. This kind of practice is a healing balm. It rarely feels like a "should."
As I have grown in program, I've been influenced by spiritual ministers and others on the recovery path, who continue to study the practices of prayer and meditation in the Twelve Step community. From them, I learned that that Bill W and his mentor came to the conclusion that Step Eleven is best practiced early in recovery. They shared that the basics of Step Eleven are best introduced by Step Six. I found that prayer and meditation was essential in the process of developing an understanding of that Universal Spiritual Power that brought me back to sanity.
I am happy to cite my sources and so glad that what I share here need not be officially sanctioned.