I never stop learning, so I would choose "infinite".

Mastering? Becoming a proficient in any technology itself, takes time. A technology in use, gets updated often so, its important to keep yourself updated (which is a very difficult task). You learn a technology if you need to use it and in that way you get hands-on-experience and get better at it. But, to master any technology, you need to spend years working on that technology. Still I doubt, if one can ever master any technology (might be an expert, not a master).