Thanks for the responses.

I realised that the limousine bus actually has a fairly limited schedule early in the morning...I basically had one option I'd have to make and then I would be cutting it just too fine with the next one.

I managed to change this ticket to HEL-NRT-MEL with the short connection.

I could also have gotten the LHR-HEL connection same day but instead I'll make my own way to HEL a couple of days prior as the BA fare is just £70. Getting a large taxes refund due to UK APD and other taxes.