It would matter if the deal passes parliament
It's not clear if a full legal text will be ready on Saturday or just a political declaration. If the text isn't done it makes a deal less likely because members of the ERG said they won't support it. However if it passes anyway, there may not be enough time to get it done and/or to implement a deal.
The EU is saying here is that business could continue as normal until that's worked out and that the deal would go into place when it's ready.
