I,ve been told to just leave a bud on it and just put it under 18hrs of light
let me know
24 hour cycles for sure. You don't need any dark periods when you are trying to change the hormones back to vegetative growth.
Add a 1/3 strength veg fert mix with some rooting hormone in it. I like
hormex for this.
http://www.hormex.com/
You need to leave a good 1/3 of the plant - this means the last few nodes/buds and a decent bit of leaves and buds below a harvest line.
You can definately take your good stuff and most of the secondary buds - but a decent bit of the plant needs to be left.
Don't cut down to a handful of nugs - leave the bottom 1/3.
Here is a plant I successfully re-veged - the one over on the left was JUST put back in, there is no new, post-flower growth there. Also note I am not blasting it with light - it is getting the ends of those make-shift t12-arrays and a pair of 23w CFL's overhead.
The plant on the left was harvested the day before this photo was taken.
Here is new growth.
This takes about 3-1/2 weeks. Be patient. More lights/more fertilizer will not help or speed this up.
Post back with any questions.