National Library is the closest subway to Hubei Hotel. With an on-time 16:00 arrival into PEK on Sunday, let's assume you'll be at the hotel checking in around 18:30. If you just toss your stuff in the room and then head out around 19:00, yes you should be able to get a taxi to the Houhai/Drum Tower area and since it's Sunday, not get too jammed up in traffic between the two. I assume you had a specific restaurant in mind.

I'm also not big on the idea of the TOH and Great Wall on the same day but if those are your top priorities, it can be done with some compromises. Because days are short, you need to get moving reasonably early.
Compromise #1: Go to Badaling which makes more sense geographically and time-wise. By private car, it is about an hour's drive from your hotel. While Badaling gets panned compared to other GW sites (mostly due to reconstruction and lots of tour groups), it has its uses and isn't all that crowded during this low season time of year, plus it opens reasonably early (by 08:00). So if you arrive around 08:00-08:30, spend 1.5-2 hours on the Wall which is likely to be enough in the cold weather, return to central Beijing by 11:30 and get dropped off at a restaurant for lunch before the main lunch rush hits. Restaurant should be somewhere geographically logical vs Temple of Heaven.

Compromise #2: Go to Temple of Heaven post-lunch. While the typical recommendation is to go first thing in the morning, mostly to see the "people activity" in the perimeter park before entering, in winter most locals don't like to get out early (or at all). In fact, if it's not bitterly cold, you're more likely to see them in the middle of the day. The TofH buildings don't care what time you're there. You can have driver drop you at West side, walk to East side, hitting the high spots which are in the middle. You only really need a couple of hours inside the TofH complex. So I suspect you will finish up around 15:00-15:30. If you want to hit up some souvenir shopping, Hongqiao Market is just across the street from the east gate. Alternatively and especially if you keep the driver all day, you can scoot to something else, maybe Jingshan Park for a dusk view (if the blasted smog dissipates).

I would follow up with a nice dinner somewhere, maybe Beijing duck? Forbidden City on your half-day: remember it's closed on Monday and you need your passport to buy a ticket. Normally they now want advance ticketing due to capacity controls, but this time of year you can buy as a walk-up without fear of sell-outs.