You are parked on a single yellow line on Bouverie Place, Paddington, which is in CPZ B7. According to the map the restricted hours are Monday-saturday 8.30am to 6.30pm. Here is the sign on Lancaster Gate as you approach the left turn to take you up to where you parked. All the Westminster CPZs are large and if there are no repeater signs anywhere, could be appealed on that aspect. However Westminster will never give way, so you'd have to take them to London Tribunals with the full PCN penalty in play.
It is very unwise to park on a single yellow line in central London without first finding out what the restrictions are. Lack of sign does not mean there is no restriction, it is almost certainly in a CPZ with signs at the entrances to the zone. A CPZ controls the single yellow line restrictions so a council doesn't have to put signs up by all the yellow lines.
Here are the applicable webpages on the Westminster site: -
Learn about the price of parking in Westminster, including any changes to tariffs.
