How do I know how much time of videos I have translated?
Thank you for your question, azfadid.
The activity page lists everything you have done on Amara. Open the subtitle sets you have made, note for each set the duration of the video, then add them all.
This is the only way I know. However, if you are asking about subtitles you have made for an On Demand team, maybe the team admins have a simpler way to know that: it's worth asking anyway.