The phrase waiting time is both natural and common. The phrase wait time is sometimes used as well.
Ngrams shows that waiting time is the more prevalent of the two, but wait time has been gaining traction for the past couple decades.
As for the verbs and prepositions you've used, those are fine – English has quite a few verbs that can be (and are frequently) used in this context. If the original wait time was 17 minutes and the new waiting time is 7 minutes, you could say any of these:
The waiting time was...
- reduced by 10 minutes
- decreased by 10 minutes
- lessened by 10 minutes
- shortened to 7 minutes
When the numbers are 20 and 10, you can use either by or to, because the wait time is both reduced by 10 minutes, and to 10 minutes. Therefore, either preposition could be used in that special case, but those two expressions – while both true – would mean two different things.
Yes, it is possible to use "ever since" with the present perfect. "Ever since" links two events, a cause event and something that is true from that point in time onward. This is actually ideal for the present perfect tense because one of the uses of the present perfect tense is to indicate that something which began in the past is still relevant in the present. An example of this use is your sentence:
"I always thought it was wrong, but ever since I read it, I've been more confused."
Using the present perfect with "ever since" shows that the speaker has been and is still confused by something which they read in the past.
With the past simple tense, as in your last sentence, it would be more appropriate to use "once" instead of "ever since". This is because "once" links a cause event with something that changed, but does not necessarily link to the present.
Once I did that, it stopped bothering me.
This sentence shows that the speaker was not bothered by "it" as soon as they did "that". It however gives not indication of whether this continues to be true in the present.
I saw your edit, if I understand right you meant to ask if it is possible to use "ever since" and present perfect without past simple, which would look something like:
"ever since" + present perfect + present
Ever since I have been pregnant I feel sick each morning.
The answer is no, this is not natural English. This structure may be encountered in informal English, but it is more natural to have the structure:
"ever since" + past simple + present perfect
Ever since I got pregnant I have felt sick each morning.
Best Answer
Long time no see probably derives from pidgin English spoken by Native Americans or Chinese immigrants, although no one is completely sure.
It matches the Mandarin Chinese phrase 好久不見 (hǎo jiǔ bú jiàn) word-for-word,* which is grammatical in Mandarin.
When you say long time no see, you are pretending to speak broken English, fitting English words to a foreign or pidgin grammar. The phrase is used so much, many people use it without knowing that, but to native ears, it certainly sounds like pidgin English because of the ungrammaticality you noticed. A few other pidgin phrases have gained some currency in English, such as: look-see, from Chinese pidgin English, as in "I'll have a look-see"; savvy to mean "understand", as in "You savvy?", probably from West African pidgin English; and da kine, Hawaiian pidgin English for "the kind", but meaning pretty much anything, or sometimes "the original kind" or "the best kind". To retain their distinctive character, these phrases don't adapt to English grammar; they retain their own grammar even when included in English sentences. Sometimes people modify long time no see, retaining the pidgin grammar; for example, long time me no see you girl.
*Ignoring the usual subtle differences between corresponding words in different languages.