I think you should have a go at both.
On the first:
London Councils guidance on timing:
Where a time restriction applies, CEOs should not issue a PCN less than two minutes before a restriction starts or less than two minutes after the restriction has expired. For example, if a restriction starts (or paid-for time expires) at 8.00am then a PCN should only be issued if the vehicle is in contravention after 8.02am. Similarly, if a restriction ends at 6.00pm then no PCNs should be issued after 5.58pm. It should be stressed that a vehicle in such a situation does not have the right to be in place for two minutes – this is not a grace period.
There is no traffic management purpose in penalising someone for a suspension that could have ended 1 second later.
On the second, you have the defence of being parked when the sign went up.
