I would ask where you are doing the course for the requirements...
we had an unpaid volunteer do NVQ3 with us, she had to do 16 hours a week minimum, and yes it did take her 2 years, despite already having level 2 to reference to.. but some of that was not eligible as they said it had been done too long ago..(1 year, but by time ended course would have been 3 yrs old which is why!) How long..May depend on the college and the assessors.. I did mine in 9 months but was an experienced practitioner, just updating, but others on same with less experience did it in 1 year.

How possible it is will depend on setting as to how helpful they are with some of the info and how included you are in their practice , but this can be the same even in paid work. For some reason some places seem very guarded and unhelpful..so choice of setting may come into it.

so many variables as every college and area is different.. best to ask where you intend to study.. ours does an interview before allowing you to enroll on these courses and hence all this can be discussed at the time.

Good luck in what ever you decide