The ship with two salvage tugs is moving around, there’s no actual towage yet. Weather is fine, so it is not weather which hampers or delays towage, it is no doubt, fire and/or its’ dangerous consequences.
UPDATE: Two more tugs are to help with firefighting on YANTIAN EXPRESS: ATLANTIC ENTERPRISE (from NY or Halifax, not clear with this tug), UNION SOVEREIGN (IMO 9262742) sailed from Rotterdam.
Full chronology: http://maritimebulletin.net/2019/01/04/container-ship-yantian-express-on-fire-in-north-atlantic/