What is considered room temperature? Should the butter be quiet soft and the flour and sugar warmer than 65-69°F degrees (18--20°C)?
There is no standard "room temperature". Everybody assumes it to be the temperature in the place they live. For recipes with Western European or US origin, you can assume the range to be somewhere between 18 and 25 Celsius (64 to 77 Fahrenheit), but for others, it can be very different. Finns sometimes use their balconies as an extra freezer, and Indians moving to other continents notice that their batters don't ferment properly when left out at the new "room" temperature.
Deviations from that range (or within it) have different effects on your cooking, depending what you are dealing with. So if you want to research the consequences of suboptimal temperature and the optimal temperature range, you have to do it separately for each ingredient and each role it has in a recipe.
The butter temperature is relevant in two cases. When you need very cold butter (e.g. for a liaison or for a pie crust), any room temperature is far from optimal, so you should use a fridge or a freezer. When you need soft butter, the softer the butter, the better, up to the point at which it starts melting, which is closer to 30 C. So with this room temperature, you will have butter that is colder than optimal. But you also probably don't have any realistic option of getting it better (quick-heating methods such as a microwave are more likely to melt it than to get it to the perfect stage), so you just have to use it as-is.
For flour and sugar, I cannot think of any situation where their temperature matters, at least in the context of room temperature. So no concerns there, use them as-is.
In many recipes "room temperature" is a relative thing on a scale from:
frozen - refrigerated - room temperature - warm - hot - boiling - baking / frying.
For ingredients historically stored in a pantry or nowadays in a fridge or freezer, it means that you should remove the ingredient from the cold and let it warm up without actively heating it. The exact temperature is not relevant because in most cases there's a rather wide range of acceptable temperatures.
For ingredients that were just heated, boiled or fried it means to let them cool down to a temperature you can work with.
This can have an effect on:
- Butter - you let it soften without melting it. Too hot butter can ruin other ingredients like eggs by curdling them.
- Eggs - for the "perfect" soft boiled egg timing is of utmost importance. If you take the egg from the fridge it's obviously colder than room temperature and needs longer boiling.
- Milk - for yeasted recipes you want to warm the milk up to activate the yeast, but you mustn't heat it so much that you kill the yeast.
- Gelatine - room temperature is the state where it isn't set yet, but will set very quickly when chilled so it has less time to soak into things like cake sponge.
- Other heated or boiled liquids - depends on the liquid, but I mostly encountered it when you're supposed to let something hot cool down enough to be safe to handle.
For eggs and milk, ‘room temperature’ isn’t quite as significant as for butter.
For butter, you need the butter to be not solid, but not a liquid. If you had a stick of butter, it would hold its shape, but you could actually bend the stick of butter without it breaking.
This allows for the ‘creaming’ process to cut small pockets of air into the butter, which helps with rising. It’s not a liquid, so there’s no moisture to affect gluten development when mixed into flour. And it’s mixes evenly into the other ingredients, not little chunks like you’d want to get a flaky pie crust.
And that’s not to say that you can substitute cold eggs or milk when the recipe calls for ‘room temperature’, as it affects how easily they whip up, or if they affect other ingredients.
But butter is the easiest one to judge if it’s ‘room temperature’ as it undergoes obvious physical changes.