The previous date of 4 February was postponed due to the need of the launch pad to be ‘re-certified’ and to have another dry run with the complete launcher.
The new date assumes that the launch pad will be ‘recertified’ by 30 January. If certification is achieved by 30 January the Sentinel-3A team will be able to proceed with fuelling the satellite on 1 February.
In the meantime the satellite has been actively checked for making sure that all protective coverings were in place and that the hydrazine fuel drums weren’t leaking. Everything related to that has been fine.
(Source European Space Agency)
Source: http://www.esa.int/