usually like 20-30 seconds if you have a good setup. if you don't have a good setup you should do a ghetto preheat by waving the gun around quickly all over the board. like I said, you want the board to be nice and warm (~70-80C) all over so you won't waste as much of your heat into the big copper pours on the inner layers. if you just jam the heat on full blast to a cold board you can end up with the top of the component scorched at ~400C while the solder is still only like 170C (SAC305 needs 220C-245C to melt) on the connections to the board since the heat just keeps bleeding away into the copper. you will learn to hate ground planes with a fiery passion, seriously fuck emc compliance and all that garbage, fuck controlled impedance, fuck dcr.
components are typically packaged in some sort of plastic package. if you solder it fast enough you can get the terminations up to 220/245C while keeping the silicon on the inside under it's critical temperature. like 140-160C or some shit maybe, forget exactly at the moment and it varies per-component.