I have two suggestions to lower the time it takes to complete an asset discovery scan.
1) If you trust that your assets are not blocking ICMP, you may want to consider setting both the UDP and TCP Scanning to "None". This will greatly reduce the time it takes for the asset scan to complete. Keep in mind that only assets that respond to ICMP will be discovered.
2) If your network topology supports it, you may want to lower your Interpacket delay. I've done asset discovery scans with an interpacket delay of 5 ms and had no issues.
I’m sorry. I do not have any best practices for completing an asset discovery scan.
Thanks for the Suggestions . In my case ,I didn't have to do much .Using the slider provided in Optimize section ,I moved it to faster which increased the batch size to 1024 and no. of sub scans to 8 .Also I turned off the Advanced UDP Scanning and as a result the scan which was 98 % in 8 hours ( A previous such scan took 18 hours) scan window ,now finished in 6 hours ad 14 minutes .Good thing is that the results are still accurate .