The lend order queue is ordered first by rate (lowest first), and then chronologically (oldest first). This means that orders placed at a lower rate will be matched ahead of those placed at higher rates. If two orders are placed at the same rate, the order that was placed first will be matched first.
You can find out how much money is currently placed at each interest rate, as well as average match times, here: www.growthstreet.co.uk/lend-order-statistics.
Your capital is at risk when you lend to businesses. Find out more here.