All new mothers need is just one hour ...

Knowingly or unknowingly, we live our lives according to certain ratios. Our work-life balance is five to two: five days of work, and two of living at the weekend. Our sleep to awake ratio is around one in three. And, if you go to work, your daily productivity is around the same - eight working hours out of 24.

Except when you have a new baby. My tiny five-month-old infant has taught me some new ratios. Once in every three hours she needs to be fed. She needs a nap in about the same measure.

My newest ratio is four in 24. I've worked out that as a new mum, I can only manage four hours of non-baby-related activity in any one day. Some of this is used up for work, as I work from home. Some of it is used up in household chores like cooking, cleaning, laundry and admin. And some for the necessary fabric of life, like phone calls to family and friends to see how they are doing.

The rest is all baby, baby, baby. Baby needs feeding, nappy changing, entertaining, stimulating, comforting. When she's cute (and she is) it is hard to work and not play with her instead. When she's grumbling (and she does), her complaints - which sound like the hard drive on your computer when it's about to crash, but at 10 times the volume - grind my inner core to the point where I cannot bear it for more than a few seconds. It's a God-given talent of babies to be able to make a noise that can instantaneously command your attention.

The four hours of productivity are hard won, cobbled out of minutes extracted here and there. On a good day, I can benefit from a few minutes of her watching her mobile turning above her, although she likes to attack the flying toys now that she can reach. Or she might happily sit up and turn the pages of her books, which in her mind are not just for reading, but also for eating. And blessed are the days when she lies on her playmat and quietly observes the details of her surroundings.

There is one thing I look forward to more than anything else now, but it is rare. All I want is an hour of time entirely to myself, no baby, no crying, no feeding, nothing. Just me.

Unless you've been a new mum (or are a very supportive new dad), I think it's hard to appreciate the sheer joy of an hour of quiet mummy-time. On an unexpectedly good day, baby's daytime nap stretches to this amount of time. Or, if a kindly relative is present to play with baby, that too gives mummy some time on her own.

Sometimes I use the hour for my own nap. Sometimes it is surprisingly enjoyable to have an uninterrupted hour to clean the house. And sometimes, it is incredibly stimulating to be able to find the woman that you once were - and to lose yourself in your work. That time becomes one of intense pleasure and sheer happiness, an hour in which you are no longer "mummy" (even my husband calls me that now). It is an hour to do something that makes you who you are. If you know a new mum, the best possible gift you can give her is an hour of time to be herself.

My time is up: I can hear baby crying as she wakes up from her nap. Now it's back to being a mummy …

Shelina Janmohamed is the author of Love in a Headscarf and writes a blog at www.spirit21.co.uk