Hello, fellow transcriber 
Your post reminded me of my attempt at transcribing a Chet Baker trumpet solo: (COVER) Chet Baker-Russ Freeman: Summer Sketch
Sure, itās difficult at the beginning, that one took me about a total of 15-16 hours. Not in one go, though. The fact that the beginning and the ending serve as a bookend helped a lot.
Iād say if youāre starting to get frustrated, just leave it for a couple of days and come back to it later. Maybe that period of āear cleansingā will be beneficial, and you can continue with fresh ears.
A few things/notions I found helpful (though their usefulness depends on the particular piece):
- The bassline can help you, they often sort of āprefigureā chord progressions or bits of melody.
- If a note seems to sound good together with a chord but it doesnāt feel 100% right, try to identify which chord it may be (root - 3rd - 5th) and play around with those options.
- At times, I found the notes almost right away, then I realized I was an octave lower (still sounded good to me). That was an easy fix.
- Try not to forget about the major scale and the minor pentatonic scale patterns/intervals. They can be useful hints. Most of these melodies are in a certain key.
- Also, at times I thought I figured out things all right, but there was still some doubt in the back of my mind. It turned out that the ārealā note was 1 semitone lower/higher than what I found.
- On the guitar, try not to expect very big jumps between strings or positions or extreme finger stretches. Try to think of āeconomicalā solutions.
Over last year, I gradually got the hang of transcribing, although I started to dabble into it before Justin published his related lessons, so my learning path and song choices are somewhat different than his suggestions. As far as vocal lines go, I managed to crack Eleanor Rigby. Other than that, I tend to focus on horn/guitar lines.
So donāt get frustrated, eventually youāll get better at it. For the time being, Iād suggest you to try some simpler (not much more than 4-5 notes), more repetitive riffs, e.g. Sunshine of Your Love, Black Night, āitā (itās the last song on The Lamb Lies Down on Broadway, it was one of the first riffs I managed to transcribe on my own), or something else that you like.