I think there is no limit on how we can trade open positions still open on trading platforms. in my experience we can open positions for trading within 2 months and we can close as our convienent time to gain profit in trading system. and in instaforex 5 min minimum, If the account is swap free then will not harm trader also. But some brokers state very clearly that positions can be opened for this time frame. If this is not mentioned, you can keep your trade open for an unlimited period of time.