You honestly think that announcing it at 4am would work at all?
An example of do nothing is this. When we had the bad snow in 2011, South West Trains tried to run a normal service. I woke up between 5-6am. I went online and looked to see how the 6.31 to Clapham was doing. It was listed for a time as running late. Suddenly it vanished never to be seen again.
There was no real train times to check back then so no way of know what had happened to it. It was at that point that I thought, ok I won't be going anywhere today.
Interestingly they managed to run trains to Aldershot from Guildford for a time. They were less affected than London. Then the next day they did implement an emergency timetable, even though by now it wasn't snowing much. However, suddenly all the trains that were running to Aldershot the previous day were not. So you have some inconsistancy on top of the previous days problems.
Thus I think it's best to tell us in advance and do what they are doing. Sure if they can see room for tweeking the times in future then that's a bonus.