First bottle

Rachel • 24, Hull UK 🇬🇧 Expecting baby number 1, 👶👑 my little princess due 29th February
My LG is 4wks Old, I've just given her her first bottle of formula, in the hopes that she will sleep longer through the night. I made up a 5oz bottle in the hopes she would drink about 4oz, whenever I have pumped breast milk during the day for her she takes 3-4oz. 
Unfortunately she only drank 2.5oz. So that has squashed my hopes of her sleeping longer but I was wondering how long I can keep the left over milk? I heard an hour but wasn't sure. It hasn't been stored in a fridge and heated up, I made it fresh when she woke for it. (I'm asking because when on the breast she's  waking up every 1.5-2hrs to feed, hence the switch to formula through the night)