From a health perspective, it doesn't really matter whether she breastfeeds for five minutes or an hour, as long as baby is gaining weight well (four to seven ounces each week for the first month, and then one to two pounds each month through month six). Some babies simply take longer than others. Baby may get more efficient as she grows, so you may (or may not) see the length of feedings shorten a bit in coming weeks.
If baby has been taking a long time to nurse because she's falling asleep often, she might have a shallow latch. Latching baby on deeper can help your breast milk flow much more quickly, keeping baby interested and allowing her to finish up sooner. Breast compressions can help if baby isn't actively drinking during her time on the breast.If baby is gaining weight slowly (or losing weight), you should seek hands-on assistance to help teach baby how to latch and/or suck more effectively.