The legislation sets out no time limit for response in respect of box junction ("moving traffic") offences. However, London Tribunals have formally stated that they consider any delay in excess of 3 months to be unreasonable and so that serves as an unofficial deadline beyond which the council would generally have to have good justification.
Concerning that you did not receive a confirmation email. The good news is that you are still within the deadline for making representations.
Not sure what the best way forward is here - whether to resubmit the same ones (be sure to take a screenshot or two while doing so if you do), or to follow up with WF somehow to check if representations were received. See what others think, who might have a better handle on internal processes.
Deadline for representations would be 25 March by my maths (28 days starting with presumed date of service, 26 February).
Worst case scenario, if you were willing to swear that you submitted representations and WF sent you a Charge Certificate you would be able to reset the process on the grounds that you submitted representations but did not receive a Notice of Rejection.
