Is it correct to say something in present tense, but it has a time information that will be taking place until a certain time in the Future.
I can't do it for the next 5 hours.
It depends on what you’re trying to express. If you mean it will take more than five hours to do, then the expression would be something like: “I can’t do it within the next five hours.” Your sentence, “I can’t do it for the next five hours,” is fine if you mean you won’t be able to get to it until five hours from now.
This is general negation not in simple present but with timeless modal, CAN and " for the next five hours " is an adverbial phrase with no discernable impact on 'my doing'. This sentence makes use of the adverb phrase like general adverbs like 'continuously', ceaselessly or uninterruptedly and, "for the next five hours" is an exacting elaboration of this continuity. It would be unfair to relate it with the verb which is by no means affected by it. The time factor has no direct bearing on the verb which expresses only an ability/possibility with the use of MODAL AUXILIARY, "CAN". When we use modal auxiliaries like CAN/COULD, it is in irrealis mood, subjunctive mood or timelessness. To be precise here's an action or state which is hypothetical or anticipated rather than actual including wishes and commands. The modals (as CAN ) may refer to probability, uncertainty or tentative ness of the present, past or future. Time of action is not important at all.
There had been a time,— will, shall, may and CAN— did exist in present and past but now their past forms exist in their own right and historical tense connection is remotely echoed in backshiftng in narration change. In englishforum.com in a discussion about timelessness of modals, it is succinctly remarked some modals (they're four) are tensed in form but tense less in usages.
Our instant example negates the time factor; it can as well admit of the same continuation and would remain as usual irrealis as time and aspect of the verb is not kindled since modal CAN expresses the ability of a probable action.
The action is not in the present, nor would it happen in the future ; it is an expression of your inability. In subjunctive expression time aspect is inconsequential — for the mood of the verb is timeless with the use of CAN.