I need to ask two questions. Can I ask this in the same post or different posts? These questions were based on the same tags but they are entirely different. Last time when I asked a question I got a reply in comments as one questions per post. Today when I tried to post two different questions I am getting "You can only post once every 20 minutes".
One question per post and yes, you have to wait.
If you ask more than one question per post, how are answerers (and the community at large) supposed to handle it?
- What if they only have an answer to one question, but not the other? Should they answer it and not address both, or should they not answer because they can't answer both? That would deprive the community of a good response to a good question.
- What if both questions are duplicate of other questions? Which one should be used as the duplicate target? No matter which one is picked people looking at the question will only be confused as the duplicate doesn't address the "other" question.
- What if one question should be closed for any reason and the other shouldn't? Should we close it or leave it open?
- What if I think one question is good and want to upvote it and the other is bad and want to downvote it?
- What if someone finds your post via Google and thinks it will solve their problem, only to find all of the answers are about your other question?
Effectively, you are just marking it harder for the community to handle your post effectively. Each question should be able to stand on its own and be judged for its own merits. Similarly, it is better for you as you know that answers will directly address your one question and not parts of your question.
All this being said, there is some flexibility for two very closely related questions in the same post. And I don't mean closely related in that they have the same tags, but closely related enough that the same answer can address both question. However, I would not recommend you do this unless you have enough experience to judge just how closely related the question are.
As for the time limit, that is there as a spam prevention measure. The rate limiting effectively limits how many questions you can ask in a time period and also how quickly you can ask them. You can reference The Complete Rate-Limiting Guide for everything but you are getting tripped up by the 1 question per 20 minute limit. Fortunately that is a temporary one that is lifted once you have achieved a minimum rep of 125.
- Users with < 125 rep, 40 minutes since their last question anywhere on the network (This applies to the user's IP address, not their account. If the user shares that IP with other users, they can be limited by the other user asking a question anywhere on the network.)
- Users limited by Anti-Recidivism System, one question per week
- Users limited from asking questions for 1 – 7 days based on the performance of their previous questions
- Users with < 10k rep trip Captcha if more than once per 60 seconds
- Users with > 10k rep trip Captcha if more than once per 30 seconds
- On Stack Overflow, Super User, Server Fault and Math (not active on all other sites)
However, a side effect of the rate limiting also helps guide new users in how to ask good questions. Asking a question is not supposed to be a rapid fire exercise. Do not just throw out two or three quick questions and hope that someone gives you an answer. We expect users to do their research and finally decide to ask on Stack Overflow after they have exhausted every option. And then writing a good question should take time. And usually the act of writing a question actually help your research because it might give you more thoughts on additional keywords to include in searches. Additionally, Google is your friend in these matters. You'd be surprised how many questions are easily solved by searching the exact title in Google.