Another beginner here. My very first straight razor shave was from a cartridge to a straight razor (least you used a shavette before switching) and just to do a WTG 1 pass shave it took me roughly 35 mins. So you're absolutely fine on timing. Now I can do a 2 pass pass shave in about 17 mins, 1 pass in 7. You'll know everything's working like it is supposed to when it doesn't pull, smooth finish etc. Take it slow and you'll see the results you want to see in time.
With the regards to the neck many have already stated it before but reiteration is good. That's probably some error in your technique that needs to be corrected. No big deal just really focus on that angle, stretching the skin really well and take the time to map out the growth for a really effective shave.
I still learn something new every shave I do and I've been shaving for a total about 5 months (I grow a beard in late fall/winter.) You'll get it; take pride in doing something not a big number of men do.
-MusicMan95