Amateur astrophotography is not directly comparable. For a start, exposure times for earth-based telescopes are limited to a few hours by the rotation of the Earth. Also, they are limited by the accumulation of noise from light pollution and thermal sources within the telescope. I would imagine that film-based astrophotography with specially treated film is limited to exposure times of up to one hour and, perhaps, no more than 20 minutes for most amateurs.
Digital astrophotography is even more susceptible to thermal noise, with sensors needing to be cooled for long exposures. Most amateur astronomers take a series of short exposures of, say, 10 seconds using uncooled sensors and then use software to stack the best frames to make good-quality final images.
I've no idea what exposure times advanced amateurs (and professionals) use for larger telescopes with apertures of, say, one metre and high-performance digital sensors with electronic (or liquid) cooling. Even here, exposure times will be strictly limited by field rotation caused by non-equatorial telescope mounts (unless you have the luxury of mechanical correction). I would imagine that stacked short exposures are used since the results can be so spectacular.
'Sir, please,' she said ... 'Will you not share your wisdom with us?'
'I have no wisdom,' he told her.
'Your experiences, then?'
'They have been trivial, uninteresting, and full of error.'
Ian M. Banks - Feersum Endjinn
It Ought to be Easy | Greasemonkey scripts