My gal only use about 10mins each feed and can last about 2-3 hours when shevwas 3mth old. Now she is 6mo, she use even lesser time. Till now she is not introduce to bottle. Like you I kept thinking I got low supply, but in actual fact, is all becos we keep feeding hourly, our milk does not have enough time to show you that they r full. dont stress yrself, if yr gal is growing well, that is the amount she need. Unless you want excess then you need to pump after each feed to build the excess.