Code:
tonumber(scanText:match("every (%d+%.%d+) sec"))
tonumber() seems to be handing a
nil return fine as of WoW 5.0.4. Also note this would only be able to match on an enUS client, labels would be different in other locales. For more information on patterns and also functions that use them, here's a link to the official
Lua documentation on it.