- Symptoms will develop within five to six days after contracting the disease.
- Symptoms will develop within six days after contracting the disease.
What is the difference between (1) and (2)? They both mean before six days have passed, don't they?
What is the difference between (1) and (2)? They both mean before six days have passed, don't they?
The difference is that "within 6 days" is a clear and logical statement which means "at some point in time between now and 6 days from now", while "within 5 to 6 days" is an ambiguous statement with no single clear definition: it could be a sloppy way of saying "within 6 days", or it could be trying to convey "between 5 and 6 days after", or it could even be a sloppy way of saying "within 5 days". Unless you can read the author's mind, you can't know which meaning was intended.
In direct answer to your question, yes - they both mean before six days have passed. However, there is a clear difference.
Cambridge defines 'within' this way:
inside or not further than an area or period of time:
So, it can mean two things - inside two given points, or no further than a single given point.
(a) Symptoms will develop within five to six days after contracting the disease. This statement indicates a range of possible times for symptom onset. Symptoms could show up as early as five days after contracting the disease, or as late as six days.
(b) Symptoms will develop within six days after contracting the disease. This statement sets a maximum window for symptom onset. Symptoms must appear within six days, but could potentially show up earlier than five days.
Therefore, while both sentences might be interpreted similarly in casual conversation, they convey slightly different information regarding the precision of the timeframe.
Symptoms could show up as early as five days after contracting the disease, or as late as six days.
I think this is just a way of emphasizing the imprecision of estimates like this. I often find myself writing things like "around 5 or 6 years ago", which is clearly redundant: "around 5 years ago" already expresses that it might not be exactly that many years.
Biological processes are highly variable, so it's hard to be precise about how long something will take. "within 5 to 6 days" might mean that it's usually within 5 days, but occasionally 6 days. So if you don't experience symptoms within 5 days you're probably safe, but don't be too surprised if they appear the next day. But if you make it to 7 days, you're very likely to be safe.
You can take a hypothetical example to test how you would receive the information. When Covid was a concern but between lockdowns, this was actually somewhat commonplace and real. Scenario:
A highly contagious, painful and chronic infection... Symptoms will develop within five to six days after contracting the infection.
The other answers suggest that it sets some kind of lower bound, however implied it may be. I'd argue that it adds absolutely none - the point of medical information/language is to be as clear and as precise as possible with something that is inherently non-deterministic (in biology there will always be outliers). My answer is therefore that they are the same - it's no different to "within six days".
Without symptoms I'd take "Symptoms will develop within five to six days after contracting the disease" on day five as being "I'm in with a shot here to dodge this one" and after day six being "Ok, I made it". If I had any kind of symptom at all, no matter the period after exposure, I'd be really concerned. Add to that, "will develop" suggests that asymptomatic infection is not possible - you will have symptoms if you're infected.
I'd argue that "symptoms typically appear between five and six days after infection" is a far-better representation of the information if indeed they wanted to set a lower bound and suggest that two days just isn't practical in linking my party attendance and my feeling unwell. There will always be outliers, but I think the general public understands this about incubation periods even if only instinctively, and it is much better at setting expectations.
Anecdotally, I have seen (and been confused by) a policy that said that something was requested "within 3-6 months". I initially took it as a suggestion to wait at least 3 months, but asked for clarification, and was told that 3 months was not a minimum.
It is confusing because logically, "within 6 months" would have conveyed the rule more precisely. My interpretation is that people may be "imprecise" because they are simultaneously indicating a maximum and an expected typical amount of time. (That is, normally 3-6 months is expected, and 6 is the maximum, but 3 is not a minimum.) So, "within 3-6 months" in this case probably meant "within typically at least 3 and definitely no more than 6 months".
Symptoms will develop within five to six days after contracting the disease.
Adding to Martha's, Bamar's and roganjosh's answers: let's charitably interpret the speaker's phrasing, that is, assume that they aren't being sloppy:
Perhaps because they simply can't recall, or maybe due to the literature being conflicting, they are unsure where exactly between the 5th and 6th days the symptoms' onset's upper bound is.
If they had meant that the upper bound is variable between the 5th and 6th days, they would have simply said “within six days”.
“Within five to six days” technically must have the same lower bound as “within six days”: symptoms could develop as early as immediately.
In all likelihood though, the speaker is being sloppy, in which case I think nschneid's answer is on to something: the speaker is probably trying to say that symptoms will develop within six days—typically between the 5th and 6th days.