Sounds to me that they are looking for a quick win in January from the EU to force the hand of the CMA and put pressure on the FTC if they go ahead with a lawsuit.
In other words, the European Commission must take a clearance decision as soon as the serious doubts of a case have been removed. If that 10 year remedy is enough to remove those concerns, then the EU could perfectly approve the deal in January and not in April.
That would allow MS to close the deal in the EU in January.
This could also be useful to pressure the CMA to take a similar decision because the markets and issues analysed are very similar to the ones in the EU and the timing would fit too (the CMA will publish provisional findings in January). So, if there are so many similarities and the EU is happy with that remedy, why not something similar in UK?
But I think that this move could have the FTC as a target. If MS can close the deal in Europe in January and the FTC wants to challenge the deal, now they would have to file a motion for a preliminary injunction in federal court along with its complaint (because there is a real risk of the merger closing).
That process is shorter in time (4-6 months). In that case the ability to litigate (or just threaten to litigate) within the deal time (July) normally improves the parties' negotiating posture with the agency over remedies and ultimate clearance. And if it doesn't, you probably have enough time to litigate without renegotiating the outside date.
But if the FTC challenges the deal and MS has to wait at least until March in UK or mid April in Europe to close it, then the FTC has no incentive (or even the ability) for a preliminary injunction, they would be less pressured for negotiation and they could take the longer path to litigation. So long, that MS would have to renegotiate the merger agreement if they still would want to go ahead.
I'm just speculating, but I think that could be one reason why all of a sudden they are looking for a fast approval with the EU: because they want a double domino effect.
It's not a bad strategy and it has been successful more than once in multi-jurisdictional reviews, specially when the FTC can be the last big obstacle