English "Come here by xx"

Basically it means "come here on or before 4pm".

You must also take into consideration what the purpose of the "come" for this "time frame" setting.

If it is a "submission deadline" or "delivering something", then it is ok to come even in the "morning", but if it is a meeting schedule with someone, it will be unreasonable to come at 10:00am even though this reply say "come here by 4pm" which literally mean any time before 4pm; so a more reasonal time to "come here" is about 15 minutes before 4pm.

Some "front-desk" of business may stop receving at 4pm in order for to allow staff to process incoming mail/delivery for another 1-2 hours before end-of-working on that day, so people will say "come" or "deliver" it "by 4pm" to mean we will stop receiving at 4pm.

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╰/) ⋈ (\\╯

大家新年進步~

come here at 4pm
意思係不遲於下午四時

by+時間名詞

意思:“到…時（已發生某事），此時謂語多用完成時；
最晚、不遲於…，在…之前”

例句：by now/then/this time/next Friday/the end of/three o`clock等。

hope it can help!

2015-01-06 15:39:39 補充：
Happy New Year! :)