It seems your wife knew about the restriction, but got the time wrong. Frankly, 5 minutes is unlikely to be considered de minimis at London Tribunals, the only place where you'd get an unbiased judgment. The council keep all your money if you pay so are hardly unbiased.
Your wife turned right into the restriction and Newham have erected an advance warning sign, so one has to conclude that the signage is adequate to convey the restriction, the test in Regulation 18(1)(a) of The Local Authorities’ Traffic Orders (Procedure) (England and Wales) Regulations 1996
