I would like to point out that I don't have a problem with doing the oiling etc in principle but I do think that if you pay for installation they should do the oiling and/or talk you through the process before you use it!!
I know that you often have to oil these work surfaces on an ongoing basis but I don't think the work surface should be installed in an unusable state or that I should have to go through all of the information on every piece that has been installed to find out if I need to finish off the job!
There is some truth in this.
There are many timber products out there that require zero treatment when installed but there are some products that do require treatment the instant they are fitted or even prior to.
Whilst I think it is a tad naïve on the customers behalf, 95 percent of the onus should be with either Ikea or the fitter. I find it astonishing that the fitters never once informed the customer that once the work-top was unpacked that it would require protection.
If the oak worktop has been cut to take the sink, the sink will need to be removed so that you can access the bare oak for oiling. It will need several coats to fully seal the oak, just as you would for the working surfaces.