Web forwarding records require "A" records pointing to 184.108.40.206. By default, they have a TTL of 300 seconds. The reason a TTL of 300 is used is to reduce downtime in the event that you delete the web forward.
Once you delete the record, it's gone from the web forwarding servers but the "A" record pointing to 220.127.116.11 will still be cached at local (recursive) DNS servers for up to the value of the TTL, which is 300.
As a result, some users will still to connect to our web forwarding server for up to 5 minutes and not receive answers (as the record has been deleted). If the TTL were higher, the duration of that outage would be longer.