Weplab is compatible with any packet log file in libpcap format. I don't know if airsnort logs packets in pcap format or not.
Anyway you can capture packets with weplab and if you can flood the network or the traffic is high, you wont need to wait 24 hours, just 30 minutes to capture 2M packets.
Weplab should break the key with the FMS attack in less than 2 hours.
You will find a draft of README file in
http://weplab.sourceforge.net/files/README
If you still want to know if your airsnort captured packets can or not be used, just try
weplab -a --debug 1 ./pcaplog
weplab -a --prismheader --debug 1 ./pcaplog
Use the method explained in README to know if you need prismheader or fcs