I have found a few web sites that parrot the 900 C cleaning cycle thing, but that temperature is very near the maximum for the heating elements and I'd need to see some better documentation before I'd believe it. (None of the sites gave any source citations to credible authorities.)
Our somewhat dated oven takes about 20 to 30 minutes to preheat to a typical 375 F so a rough extrapolation estimates about an hour (at full power) to come to the 600 F. A cleaning cycle for that stove heats for about an hour, and "sustains" for roughly another hour with the heater cycling on/off, but the oven stays locked for a little more than another two hours while the oven cools down to where the door can be opened. Total cycle a little over 4 yours, more than half of which is spent cooling down.
Outside surfaces don't seem to get above about 150 F for any of ours, but they might go a little higher on one enclosed in cabinetry.
Even if you don't use the self-cleaning feature, an oven with that capability will have more insulation, and claims that normal cooking will be slightly more economical probably have some basis, although it's hard to generalize. In the US, new appliances have an "energy rating" that's probably a better guide. Sources that claim the better efficiency also suggest that using the cleaning cycle more than about monthly will probably obliterate any savings, since the cleaning eats lots of watt-hours, but they don't give any basis (how frequently do you bake?) for that recommendation.
Some sources do warn that you should move your small birds out of range while doing a cleaning, and the truly paranoid recommend covering acquariums and turning off the air pumps due to the "noxious gases" produced by cleaning. Some exotic birds are sensitive, and might be affected by the small amounts of gases produced -- perhaps(?). There is sometimes a slight "odor" from running the cycle with ones I've used, but that does also depend on how dirty it was (and what the spills were). I never noticed any adverse effect on acquariums that I used to have (they were so overpopulated that turning off the air even for a little while would have killed everything; and we've never (intentionally) had birds in the house to observe. (When the cats occasionally brought one in and turned it loose we weren't cleaning the oven.) Turning on the kitchen exhaust fan for a while, if you have one that exhausts outside and if you have any reason to worry, or if the slight odor bothers you, would seem sufficient from what I've observed.