It’s a good question, but does it really needs to be answered?
Do you imagine a professional trader trading like an amateur?
No, a pro trades in professional conditions.
Okay, it can be fun to trade from your smartphone, it can be useful to follow positions, or if your desktop is down, if no other choice in exceptional circumstances..
But if you want to trade as a pro, remember that it is dangerous.
It does not make sense, markets are volatile, there are different markets opening through the day that influences market prices..
To work like a pro you will need several screens; each screen has its own usefulness
Having several monitors is not a luxury, it will give you an advantage; you won’t waste time searching for the information, to be efficient everything has an importance in trading.
For the broker if you trade from your desktop, mobile or smartwatch its the same! But for you what is the professional way? Do you have an advantage? Are you operating at your best level? NO
Never forget that on the markets you are in competition with the most brilliant minds in the world, if you work like an amateur you have 0 chances to win against them.
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what is a reasonable needed duration to become a professional trader?
Realistically, Neither 1 month or 2, or even 1 year.