I haven't tried market order after hours, but I bought 1c above the ask price b4 (after hours) I wanted to get in ( pissed so many times for penny pinching on my entries, then next morning, I'd look at the market running away from me.
This is an Exchange/ECN restriction. The reason for is to limit complaints and market manipulation in off hours when liquidity is limited and Regulation NMS might not be enforced. What I suggest my clients do is use a limit order no more than 10% away from last price, as any more will be rejected. An example of a hotkey/hot button would be Buy Ask +.20 or Sell Full +.20 to send an aggressive buy or sell order that is still compliant. The buy ask +.20 for 500 shares looks like this using ARCA. This can be used from 4am et to 8pm et. It can be used as a hot button or if you assign a key board combo, a hot key. Below that is sell full using ARCA targeting $0.20 below the bid. These are very easy to set up and test.
Robert and others - thanks much for taking time to clarify this. You guys are great and this was very helpful. It makes complete sense given the high volatility and low volumes during extended hours - a market order is a pretty risky proposition with no guarantees to the price or even if the order and how much of it will be filled. I tested limit orders with IBKR during extended hours as suggested and they seem to work fine. BTW - Robinhood has this on their website : "If you place a market order during extended-hours (9:00 to 9:30 AM or 4:00 - 6:00 PM ET) your order will be valid during extended-hours. If you place a market order when the markets are closed, your order will queue until market open (9:30 AM ET). We automatically convert most market buy orders into limit orders with a 5% collar to help cushion against any significant upward price movements. We also convert most market sell orders to limit orders with a 5% collar during extended-hours, to help cushion against the increased volatility of the extended-hours session."