How does putting a の at the end of a sentence change the meaning?
For example, here are some sentences:
明日何時に来るの What time will you come tomorrow
昨日何を食べたの What did you eat yesterday
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Generally speaking a sentence ending in の will be less formal equivalent of the "の／んです" construction. Hence:
Questions ending in の, as in your examples, are less formal equivalents of the same questions ending in んですか.
Questions ending in the plain/past form are less formal equivalents of (in your examples) questions ending with 来ます（か？）／食べました（か？）
1) I have assumed you are familiar with the use of "の／んです vs です／〜ます" but for reference:
"When んですis used in questions or in the でしょう constructions, it is used to express one's conjectures on the basis of what one has heard or observed" eg 雨が降っているんですか〜"Is it that it is raining" as opposed to "Is it raining" (ref below)
2) I have also assumed your focus is on questions: Sentences that are not questions using "の／んです" (and its variants) are used for explanation, rapport, reproach and "backgrounding". This is covered in the same reference given below. [I would classify "soft sounding affirmation" discussed below as an example of rapport.]
3) Your examples are probably spoken with slightly raised tone at the end of the sentence to make it clear you are asking a question, as you might do in English.
4) If the sentence ends in か then raising your voice at the end of a sentence is less important.
5) I said の is equivalent to のですか rather than のです because I think you are less likely to hear questions asked that way but its not inconceivable (in your sentences it is clear from the the 何時に／何を that they are questions).
Ref: A students' guide to Japanese Grammar, Naomi Hanaoka McGloin, p89/90
As you seem to have already answered yourself in your own translations, "の" with accent/intonation in the end turns a sentence into a question.
Note however that if you don't put such an emphasis in the end, "の" just act as a slight softner of the sentence and doesn't turn the sentence into a question. This form sounds like a child speak, so I don't recommend you use it yourself.
今日はコーヒーを飲んだの: I had some coffee today