I agree with @lpb This is an easy way to do this. A more advanced way is to use an integration called Everhour. Their integration in asana is the best and you can manage your reporting, timeblock budget and invoice all from their website. But to do the timetracking you do not need to leave Asana.
They also use the custom field called “estimate” to pull in your estimated time and then record your actual time via the push of a button. here are some links with more info:
cc’ing @Mike_Kulakov @Waclaw_Wolodko if you want to jump in.
Other time tracking options can also be seen here: