She's at the age where distraction at the boob can begin for developmental reasons and the world is beginning to be full of toys! She's also at the age where feeds can become - sometimes quite suddenly- a lot faster. They start to become more efficient at feeding. So her behaviour isn't unusual and could be unrelated to any supply concerns. To judge supply consider her behaviour at the breast - is she clearly swallowing with a good latch, does she seem satisfied after a feed and is she prepared to wait for the next one. Look at her nappies - around 6 wet ones in 24 hours (don't count dirty ones - there's a massive range of normal) - although the wet nappies are obviously affected by your supplementing too. And finally consider her weight gain.
I would try and feed her in an environment with minimal distractions. Some people use a nursing necklace to try and keep attention forward. Don't worry about the timing too much - as long as there are periods of clearly feeding and swallowing. Some babies can get a full feed in less than 10 minutes at her age.
