The less time a trade lasts, the more attention that strategy requires.
A day trade that lasts 3 or 4 minutes requires steady focus. That trade will be exited and there may be another opportunity, or possibly the exit requires a manual action on the part of the trader. If trades last a few days, there isn’t a lot to do while that trade is happening. The trader may look for more trades, but this may only take 20 minutes a day, and then the work is mostly done on that trade for the next several hours or days.
Next, we need to consider if the trader actively manages the positions, or if they set stop losses and profits targets and then leaves the trade alone. Actively managing a trade—determining when to exit in real-time—takes a lot more focus than setting a stop loss and profit target and walking away.
All these things can be boiled down to a few guidelines:
Shorter time frames and active management require more focus. This typically means the trader is better off focusing on one, and no more than several, currency pairs. Due to the short time frame of trades, these pairs should be enough to provide lots of trading opportunities.
Longer time frames, and not a lot of active management, means more currency pairs can be traded, and may be required in order to find enough trading opportunities.
These rules are simply guidelines traders can take note of.