I can't see being able to pray for everything I need to pray for without praying for everything I need to pray for.
If I take into account just the things I should pray for - praise ot God, church, family, sanctification, marriage, mortification of sin, kings, rulers, work, evangleism, etc., I can't see prayer "regularly" being too short. Devotions in reading/studying and prayer should be a good time, but a hearty time. I think, then, if we are familiar with the Bible, and know all the things the Bible tells us to pray for (commands us) then prayer will be a longer time than a shorter time.