I am wondering what the best glue to use to attach weedgaurds to jigs, i tried superglue and it was horrible.

I use 5-minute epoxy

how long do you have to hold the brush guard in place for it to hold with 5 min apoxy?

I just put it in and set the head upright and leave it overnight and package up. Generally use Devcon 2 ton 30 minute. If I only have a few I will use the 7 min.

I use locktite super glue gel.  You don't get the white residue like with regular super glue and it seems to hold nicely.  I really like the applicator also.  It's the only super glue I've ever used that is still usable after the first couple times.  I haven't had a weedguard come out yet, but I've only made 60 or so.