It is not necessary to time feeds at the breast. All babies have individual needs in regards to breastfeeding, some requiring as short as 10-15 minutes and others may need to feed for longer. Some may only need to feed from one breast at a feed whilst others require both breasts. Time spent at the breast can also vary from feed to feed.
Recent research using ultrasound on babies over 4 weeks of age, shows that babies self regulate the time they spend at the breast. The volume a baby takes at one feed is not always related to the time spent at the breast.
Very long feeds spent at one breast may interfere with milk synthesis, as research has shown the temperature of the breast drops significantly as the feed progresses. Therefore, if baby shows the need to feed for long periods it may be helpful to switch sides several times rather than leave the baby at the one breast for a long period of time.
Before the milk comes in, when your breasts are producing colostrum, you may also find it useful to switch sides frequently. As colostrum is present in small volumes this will enable your baby to easily access the colostrum available in both breasts and will reduce pressure on your nipples in those first few days whilst learning to feed.