Position duration?

It depends on the back test. When I back test, I usually draw a profile of average cumulative returns during next few mins, hours or days when a position is opened. In real trading, I close a trade at the time when historical average cumulative rerturns profile reach it's peak

You can keep a position open for as long as you want, just keep in mind to calculate your swaps.

Literally as long as you want. Be aware of swap
xharges though.

Also, if a broker is telling you that you can't hold a position as long as you want (or as long as you can afford the swap) there is something shady about that broker.

Agreed.