I would make your schedule a little more variable. That first duration was 5s long at 4s mark. Might be too long for him now. Stick to 1-3s with stay at source. And do more 1s-2s.
Stretch from 41s-45s was nice - got 2nd mark in for staying at source.
Then at 56s, that is when I see him being unsure? His rate of reinforcement went down. So we need to get the rate back up - add more immediate rewards and only a few with duration.
Then some really nice sequences between 1:15 and 1:25 when he got back to work.
For timing of going back in, I would have marked/rewarded at 1:41 before he had a chance to come off (of course you didn't know he'd come off but that was 2s duration so that is a good limit to shoot for with him.
He did do very well on the shoe! You were getting in some duration between 1:53-1:57, just a tad late going in at 1:57 as he started to pull off. That is why I'm thinking 2-3s the max for duration right now with him.
In your next session - do more immediate rewards with only 1 or 2 with duration and the move on to the Red light/Green light game doing the same exercise.
He finds, you mark and go in. You bring hand back away and the second he stays, bring your treat hand in slooooowly. Stop if he comes to it (don't move it back) and then when he goes back to source continue on in.
We want to watch any frustration he is having. So up your rate of reinforcement if you see that occurring.
Lots of good information in this session!!