Hi there. It really all does depend on your assessment centre/course provider, and how much experience and knowledge you may already have.
I am just in the final throes of NVQ3, having taken just on a year to do it, as an unpaid volunteer. I did not have level 2 but was taken onto 3 as I "had too much life experience to go onto level 2."
I worked 3 days a week unpaid, and had 2 days a week for study, and the study part was HARD. My setting did not fully support me (one member of staff who had just done NVQ3 herself was brilliant tho!) and I did not have enough responsibility really. This was really difficult when it came to observations, and drawing up assessment plans etc. I have winged it but it wasnt right really!!! You would really need consider your option units in light of this.
If you have a setting who will coach and mentor you and maybe let you in on staff meetings and let you co-key work a child or two then it will easier for you. Lots of these things didnt really occur to me till towards the end, and I am going to write to my setting in case they ever take on another student.
At the end, yes I am glad I did it, and really NVQ 3 is going to be absolutley necessary for any career progression so go for it!
Good luck!!