I use Everhour and I love it. I’m a consultant with lots of different clients - I track each of them in a different Asana project. The integration into Asana is excellent - you can start a timer or manually enter how much time was spent on a task. You can also add a note to explain what you were doing. Then on the Everhour page you can generate detailed reports of your time or add the time to invoices. I tried Harvest but it wasn’t as good. Unfortunately Everhour is not cheap. There is no free plan and they bill for a minimum of 5 users to it is quite expensive for a 1-person team.