SLI questions

Ok here is my build first off,

CPU: I5-2400 ( I will have very minimal OC, 3.99 tops)
Cooler: Corsair A50
Mobo: P8P67-M Pro
GPU: PNY 560 Ti OC2
RAM: G.skill ripjaws 4gb 1333
PSU: Antec Truepower New 650
HDD: WD Caviar Blue 7200RPM
OD: Asus 24x DVD-RW
Fans: 1x 120mm fan no LED:rear mounted
2x 120mm fan with LED: Front mounted
1x 140mm fan with LED: Top mounted

I built this system so that I could easily expand by changing out a minimal number of parts, and I have confirmed that my motherboard will fit two 560 ti's. My question is though, with a 650 watt power supply, which has the required PCI-E connectors, will this be able to run SLI, and for about how long?