I'm honestly not crazy about this class. I don't see that it has any value not present in the following:

```
import time

start = time.time()
do_stuff()
duration = time.time() - start
```
which is actually less code than
```
from wherever import Timer

timer = Timer()
timer.start()
do_stuff()
duration = timer.duration()
```

The former is less code without even counting the fact that this class has to exist. If we were doing some sort of complex time-keeping pattern, that would be one thing. I'm just not seeing it though, so I suggest removing this class.