You would pose this as a question to ask when the event is happening - in this case booking into a hotel. You can ask the person 'what time' but you can also just use the word 'when', so 'when do we need to check in?' as this also makes sense.
You can also ask 'what time is check in?'.
To check in means to let the hotel know you are there and access your room.
これは、「チェックインは何時ですか」という質問の形で聞けます。
'what time' とともに 'when' も使うことができます。
ですから、
'When do we need to check in?'（チェックインは何時ですか）
これでも伝わります。
また、'What time is check in?'（チェックインは何時ですか）と聞くこともできます。
'to check in' は、ホテルに手続きして入室することをいいます。
「何時にチェックインする？」は友達と話している感じですね。
そういう場合、英語で「○○する？」はよく「Wanna (want to) ○○」？になります。
例えば、
Wanna do something today?
今日何かする？
また、
「ホテルへチェックインする」はcheck in/check into a hotelになります。
そして、
"何時にチェックインする？"はWhat time do you wanna check into the hotel?やWhat time do you wanna check in?と言います。
ご参考になれば幸いです！
Is an early check-in or a late check-in best for you?
When asking a person what would be best, it is a way to allow that person to choose what works for him/her.
If "specific" is used to ask about something, it calls for a precise or clearly defined answer. For example, 10:30 a.m. instead of "late morning."
It can be better to state the options in order to have a better idea of what the person wants as the example expresses, either early or late. This is best used if multiple options are available.
The phrase "check in" has three meanings when referring to travel: to check in at an airport, to check in at a hotel, and to meet up. Depending on what you mean, you may want to add on what kind of check in you are doing so that your listener understands what you're talking about. I hope that this helps. :)
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