Does an Rohloff oil wear out from the atmosphere ? If I have open bottle with Rohloff oil, can I use it for example 9 years after it is opened ?
I don't know. It is possible; see Dan's logic about the annual oil changes even at 0km. But I'm not fully convinced that hydrophillia, as Dan has it, is the whole answer. The Rohloff gearbox is not sealed against the atmosphere, so water can condense inside it and cause damage quite independently from the oil absorbing water (or not, as the case may be). By itself condensation is already sufficient cause for Rohloff to advise owners to wash out the gearbox with thin oil every year.
Furthermore, I think the fact that Rohloff sells 250ml bottles, nominally a 10-year supply for a private owner, to the retail trade for sale to private owners tells us that Rohloff is not worried about the oil being hygroscopic (attracting water) enough to ruin it. Also, there's the consideration that, if water absorption were a problem, under consumer law, especially strong in Germany, there would be a warning on the canisters to use the oil by either a sell-by date or in a given period after opening it.
There are in fact oils that do not attract water. I believe I have one (another one?) on my bike, in the brake tubes of my Magura Hydraulic Rim Brakes.
Why don't you write to Rohloff, explain your question, and share their answer with us. They're generally quite good with meaningful technical replies.
More importantly if I buy the hub now, can I keep it safe in the garage or at home, install it in half or one a year from now, then ride it another year and then change the oil ?
No, you shouldn't. Your guarantee starts from the date on the sales receipt. So within the first year, even with 0K because the box is sitting on a shelf in your garage, you should change the oil to protect your warranty. And just in case Dan is right.
Explain your plan to Rohloff when you're writing to them, and ask them a) whether they're willing to extend your warranty from when the box is fitted to the bike, b) whether you should change the oil annually while it sits on the shelf, and c) whether it is a good idea to ride a brand-new box for 5-6000km before the first oil change or whether some shorter period in the first year only wouldn't be a good idea to clear out metal particles knocked off the gears of a hand-finished box at the beginning of its service-life.
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There is no rush to buy the bigger containers of oil. Unless you're going to buy a couple of syringes and screw-in tubes separately, it makes sense to buy a couple of the 25ml full service kits first so that you have the necessary gear (one syringe for clean oil, one for dirty oil) for the service, as Martin has explained.
