to my knowledge the danger time is when heat is going away and maybe a month after that
During the heat (+1-2 week) and two months later (58-62 day to 1-2 week) after the heat (when "in theory" calving would take place).
During the heat, the cervix is open, hormones are on the ceiling and the body is stressed. However, in such cases, the pus can leave, it can be quickly noticed and cured in most cases without surgery (especially if you are young).
At the time of "calving", the hormones are at their peak again (not in all dogs), the cervix is usually closed, but it could also be open, the body is again under strain, but not to such an extent. In such cases, in the case of a closed cervix, the problem is that there is no discharge and it accumulates in the uterus. Those who know their dog well and are aware of it will recognize it in time and perhaps it can be solved without surgery. Those who know their dog less well tend to notice it late. For them, it can only be cured with surgery if they survive.
In old dogs, surgery is almost always necessary, because their bodies/immunity are no longer as strong and the uterine wall is strongly folded inside, so the discharge sticks to it, even if the uterus is opened (with hormone injection).
The first day of heat is the first drop of blood. From here on, the heat lasts 21 days, it can last a few days longer. The cervix then closes completely in 1-2 weeks.
This is the one month period when you have to pay attention.
The "calving" is 58-62 days from the middle of the heat (when the dog would mate and fertilize), then the hormone level rises and this lasts for 1-2 weeks. This is the 3-week period when you also have to pay attention.
It usually occurs in older dogs, but it can happen in young ones (rarely). After they are 5 years old, I already give them an immune booster for the heat and the "calving". E.g. DMG.
Vetri DMG for USA.
Unfortunately, pyo is also a matter of luck. The dog can die even if we pay attention to the signs, and some people always have sex with dirty hands without bathing and the dog will never be harmed. Luck and lottery.
No need to worry, pyo is "not common", but unfortunately it is also a danger. Life as a zoophile is hard, dogs live much shorter lives and can die from many diseases, not just pyo. Stomach twisting, intestinal twisting, ticks, paralysis, tumor, etc., these are just as risky.