iMac mid-2011 How long to run hardware test with 32GB RAM

Have a mid-2011 iMac with 32GB RAM has been running ok for years and nothing recently changed in the hardware. Was purchased without HDD and a 360GB Intel SSD was installed and MacOS upgraded to 10.13 (original OS installed by me may have been Lion?). Recently it started to become unresponsive after running for a while - usually when left on overnight but one instance while I was actively using it after being on for a few hours.

Typical symptoms are:

• fans are running full
• waking up the display (by keyboard or trackpad) either just turns on backlight with nothing displayed, or showing the lock screen
• when lock screen is displayed, can usually enter password but won't progress to anything, just shows beachball
• the one instance it happened while I was using it, just became unresponsive, showing beachball

Have tried running AHT (started with 'd' key on boot up but downloaded via internet) but have not had a first pass complete yet even when run overnight. Typical result after 8 hours or more as per image (background is all blue, there are some outside light reflections captured in the photo).

Does anyone have experience in how long a pass should take to complete with 32GB?