After recording vocals tracks they playback offbeat

There is always some latency when audio is converted to digital goes into a computer DAW and then leaves and is converted back to analogue for you to here in your headphones. Hence Direct Monitoring allows you to here yourself without the latency delay when recording. ASIO drivers generally provide much lower latency throughput than the default Windows audio drivers.

Also you can check the Buffer settings in Audition's Audio Hardware preferences page. For recording the lower the number the better for latency. However go too low and your Multitrack playback may not be able to cope and go jittery or break up. So make the setting as low as possible without it affecting the audio playback. The more added effects you have on a Multitrack track the greater the buffer required. So it is usually better to track with effects turned off.