I bottled my beer yesterday and based on some research I decided to place it near heater to keep warm temps, I got the one for this specific reason. The thing is that the heater is pretty old and it has kinda active and inactive phases, the ambient temp (I put thermometer just behind my bottles) can go below 20C/68F in inactive phase and above 25C/77F in the active one. So the temperature can change by up to 5C/9F during one hour or so. Can such temperature fluctuations do any harm to the carbonation process or beer flavor? Thanks!
IMHO the minor fluctuations in temperature don't really affect the overall flavour because the beer has a thermal capacity to resist rapid temp changes. Gradual changes over half a day will affect it more.
What will probably affect conditioning most is the overall ambient temperature that the beer is stored in. Over 25C/77F is perhaps not the best temperature to condition beer. A stout or porter will probably condition reasonably well but a lighter ale or lager may develop a few more fruity flavours at temperatures over 20C/68F. YMMV. IMHO a good temperature to bottle condition beer is about 15C in a dark place over the course of at least one month. Some copper coloured ales can taste better if conditioned nearer 20C as that may enhance the overall flavour profile.
If rapid carbonation is all that is required then 20C for 10-14 days usually works well. I prefer 15C/59F or thereabout for a longer time.
The length of time conditioning is usually as important a factor as temperature. Some beers that are not particularly pleasant after a month, are wonderful after 6 months conditioning. That is particularly true of strong, dark, hoppy ales.
Some use the word conditioning to only mean achieving carbonation. I use it in the more expansive meaning of "reaching the correct condition" which takes some time. IMHO carbonation is only one part of that process. Others use the word ageing for the temporal process after carbonation. Whatever...