I think the fundamental is understanding the technologies involved,
Foundation say 5 hrs initially the later 3 - 3.5 hrs
Troubleshooting 2.5 then later 2
Full scale 7hrs initally then later 5
When going through them at the beginning don't focus too much on speed. Instead try to get a deep understanding of the interactions between the technologies. Initially might be slow, but with time will pick up speed. Also in BGP, topology tends to get big and confusing, try piece things down and understand the route advertisement flow.
For troubleshooting, try all possible solution you can think of, develop a structured approach and stick to it. With time you will get very fast naturally
At least the above worked for me.
How much time should I allocate to complete the foundation, troublehshooting and full scale labs to gauge my readiness?