Hey Matticustard,
yes, if you use pure oils it can take a long time, but there may be a reason to use the pure oil, namely if you want it to penetrate far into the wood before it hardens. This used to be done with wooden planes or planing workbench tops so they would never warp again. Young cabinetmakers were taught to Iay their new planes into a bath of linseed oil for a week or until it sinks[1,2]. But for this you had to take weeks, when you could not yet use the equipment.
There are two ways to use the drying oils with wood: Either I want the wood pieces to be completely impregnated with the polymerizing oil, in which case I use pure, unheated drying oil. I always collect the wooden things, such as cutting boards and cooking spoons, before I make such an action, so that it is worthwhile.
I once treated a very old spruce table top, about 1½ " thick, by applying pure linseed oil over and over until it came out on the underside. Then I let it dry for two months. This is an extreme example, but the finish is incredible, it looks like plastic, and the wood texture comes out very nicely. It’s very hard and I can put a wet bottle down without a coaster and the water just beads up.
Or I want a quick water-repellent coating: Then I use something called “Leinölfirnis” here. You get it from woodworker suppliers as well as from artist suppliers. This is heated (prepolymerized) linseed oil with siccatives added. The heating procedure makes it thicker, which means it doesn’t soak into the wood as well. Because of the siccatives, it begins to dry in a few minutes of contact with air, and after I have applied it so many times that the wood no longer absorbs anything, at the latest after half an hour, I have to wipe off the excess, otherwise it would become sticky and whitish and hinder polymerization. After complete drying (12-24 hours), this can then be repeated a few times, but only achieves a penetration depth of one to a few millimeters. Although it gives a good water repellent coating, it then remains possible that the wood inside still warps or soaks up water when left in the water. To make it penetrate deeper, you can heat it slightly beforehand to lower viscosity, or you can mix it 1:1 with natural turpentine oil or orange oil. They do not take part in polymerization, they evaporate completely.
Regarding food safety, if I look at the datasheets of e.g. linseed oil based Livos ARDVOS Holzoel Nr. 266, such products are approved for contact with food.