There's actually two problems with such code: one is that it doesn't actually make the code easier to read, but harder.
The other is more subtle: using constants like this is working at the wrong level of abstraction. The correct way to write this kind of code is to use a wrapper function which knows how to put together URLs, since there are lots of special rules to how URLs are put together (encoding, etc.) But a lot of people don't bother, and instead simply concatenate strings with a SLASH between them, and think that because they define the slash in some constant that makes the code correct.
Naturally, I like constants like POPCORN_PRICE = 12 or whatever. They add meaning to meaningless numbers.
I am on the fence for HOUR_PER_DAY and MINUTE_PER_HOUR, because they never change, but they at least add a certain security if you chain them together. bar = lengthInSeconds * SECONDS_IN_MINUTE * MINUTES_IN_HOUR * DAYS_IN_YEAR. In this case you can simply match. Seconds - Seconds, fits. Minute - Minutes, fits. Hour - days... wait, doesn't fit.
However, if you look at PROTOCOL + COLON + SLASH + SLASH versus "http://, there is just nothing added.
Ideally, especially if you're using a strongly typed language, you should just use time-unit types (or at least macros or inlinable functions) for that: `fromSeconds(lengthInSeconds).toYears()`, lengthInSeconds.seconds.to_year, `SECONDS_TO_YEARS(lengthInSeconds)`, new TimeSpan(seconds=lengthInSeconds).toYears(), etc...)
url = "http://" + ....
I remember working on a Java codebase years ago where every string literal was defined in a Constants class - fair enough I guess. However, it had entries that looked like this:
leading to code that looked like: