I'm making this for Thanksgiving this year. Anyone have any thoughts on how far in advance I can make the relish? Hoping to get it out of the way...

Im sure it will be fine. I agree with BakerRB, some delicata aint that delicata! Its a great recipe.

I think you'll be fine making it ahead. I haven't made this particular recipe (looks great though), but I've made similar dishes that were fine reheated. I'd put the squash in a hot oven or skillet briefly to reheat, and I'd microwave the fennel/apple sauce until very warm instead of very hot to reduce the risk that it turns to mush. I'd cool the sauce down quickly after initial cooking to - pour out on a cookie sheet or put pan in an ice bath. If you haven't had delicata squash before I'd actually recommend making it ahead since the ubiquitous description of the peel being tender enough to eat is not true to everyone or maybe not true for every level of maturity of squash. It can be quite an unpleasant texture. If you think it's too tough you can trim or peel it off fairly easily after cooking.