Every patient is different, and every knee is different, so there is no set in stone date for when you'll be able to do any of the above activities. Generally, if you listen to your knee, you'll know what it's ready for and what it's not ready for. If you have both knees done at the same time, you'll likely notice they recover differently; this could be due to the amount of damage, the amount of work the surgeon needed to do in each one, or just plain orneriness....
Also, those that have them done at different times also often notice the healing rate is not the same for both. Because recoveries are all different, we advise taking 12 weeks off work in general, although some people are back at work before that, depending on what their workday entails. Others, especially those with physically demanding jobs, may need more time, but overall 12 weeks is a good general estimate.
The same goes for working in your garden. If you need to do a lot of bending, maybe kneeling if your knee allows (many people aren't comfortable kneeling after a TKR) , and heavy tasks, it may be longer than three months; but if all you need to do is stand for short periods of time to snip a few flowers, you'll likely be able to do that as you walk outside, somewhere around a month after surgery.
Driving again depends on when you no longer need any strong pain meds as it is illegal (not to mention a bad idea) to drive while taking them. It also depends on how your knee feels and how fast it recovers. It takes longer when your driving knee is the surgical knee as the reaction time to brake is greatly diminished while in the early stages of recovery. Some people drive within weeks, others don't drive until after their 6 week post-op exam, others need longer.
This recovery takes, on average, a full year, but many people are feeling much better around the three month mark. By that time people can usually see the amount of recovery progress they've made, are mostly out of pain, other than normal twinges and so on, and are walking much more easily and freely. But, this doesn't mean those that take longer to reach that point are behind; it just means their particular knee needs more time.