How long do you think a ritual should take? Not including banishings.
Exactly 27 minutes, 13.496 seconds, except on Tuesdays, Sundays, and full moons, when you halve the amount of hours between sunrise and sunset in your location and add that on as minutes -5.
Any longer or shorter and you get devoured by hellhounds.
Okay - serious answer - they take as long as they take! 
Watch some of E.A.'s stuff, I’m also excited about RavensAscent uploading hers soon, these are REAL rituals by REAL people and they really just take as long as it takes to do any prep, call the spirit, interact or whatever…
There’s no set time, it’s not like guidelines to meditate for a minimum of 20m a day or whatever. 
Some of mine take 2 - 3 minutes, some take 45m, some take hours.
Just like Lady Eva said: it really depends. The rituals I have done have varied from 10 minutes to one being 50 minutes, meditations have varied from 5 minutes to 25 minutes. It really depends on you, what you are doing, and how quickly you can get into the states you need to get into. Like what EA has said before regarding entering states such as the Theta Gamma Sync, he can enter it in several seconds while for others, like myself, it can take several minutes.
Best of luck with your work and just keep practicing. Like anything else you will get better over time.
I’ve had rituals last 5 minutes, 45 minutes, and even some that I realized took me an hour and 35 minutes. There is no requirement for time, just do the ritual until all necessary tasks are performed and if it requires any meditation or thought immersion of the goal on your part, do that until everything feels just right to you. You will know what ‘just right’ is when you feel it. It’s something we can’t explain in words, you have to feel it for yourself.
As for my ritual videos Eva mentioned, I uploaded a few spells last night and was going to upload the first ritual I filmed however when I went to upload the video i realized after I edited it, I did not get to save the edited final version because I have been telling my computer to fuck off all week when it asked me to update some things and my computer finally said screw you bitch I’m updating anyway so it shut down on its own and started updating when I walked outta the room and I lost my unsaved changes so I gotta go back and edit the original footage again. Oh well, there were only a few parts I had to edit out where I got so into the ritual I knocked over the camera and didn’t realize it (I was in a deep trance) so there was like 3 mins. of carpet footage I have to edit out.