If you have beaten the offline time road rule on Watt St. and didn't get the achievement you also need to beat the online time road rule.
To avoid any problems with this achievement make sure you do the offline time road rule on Watt St. before any other road rules on this street. If you have done any other road rules on Watt St. you also need to beat the online time road rule.
I'm not sure whether or not this is a glitch with the achievement or an inaccurate achievement description. Hopefully this will be fixed in a patch.
Edit: This has now been patched.