Given that the weather at this time of year could enforce a very light day on him, or even a day without any riding at all, I would think that, as long as he is physically OK churning out these miles, then carry on building up a buffer. I'm aware he is behind what the overall daily average will have to be at the end of the year, but the ideal situation for Steve is to be reducing the daily requirement to the record by the vernal equinox.
If we get a re-run of last Feb/March, when it never stopped raining, or 2013, when we had those bitterly cold north-easterlies for weeks on end, he'll be glad of a few miles in the bank.