You are really asking two questions here:
- Do post-tribulation premillennialists believe that the Bible prophesies any events that can be used to make an exact prediction of the timing of Christ's Second Coming?
- If so, how do post-tribulation premillennialists square this with Matthew 24:36?
The question that needs to be primarily addressed is actually the first one, not the second. Two prominent post-tribulation premillennialists, George E. Ladd and Wayne Grudem, argue that the signs prophesied in the Bible are not of a nature that we can draw firm conclusions regarding the timing of Christ's return.
Non-dispensationalists like Grudem do not find that Daniel 9 and related passages provide evidence of a literal, fixed-length peace treaty with Israel. Rather, the signs he sees taught in Scripture that must be fulfilled prior to Christ's Second Coming are the following:
- Preaching of the Gospel to all nations (Mark 13:10)
- Probably not fulfilled, but possible in light of Paul's language in Colossians 1:5–6, "in the whole world."
- Great tribulation (Mark 13:7–8)
- Probably not fulfilled, but possible that it was fulfilled in the fall of Jerusalem (AD 66–70).
- False prophets (Mark 13:22)
- Probably not fulfilled, but it may have been fulfilled in the many examples of false prophets that have arisen throughout Christian history.
- Signs in the heavens (Mark 13:24–25)
- Almost certainly not fulfilled. However, "they could occur very quickly," on the order of minutes or hours, and thus this does not suggest that Christ could not return at any time.
- Appearance of the Man of Lawlessness (2 Thessalonians 2:1–10)
- Probably not fulfilled, but it is still possible that the "man of lawlessness" could refer to a historical figure, whether a Roman emperor or a Hitler/Stalin.
- All Israel to be saved (Romans 11:26)
- Probably not fulfilled, but perhaps Paul referred simply to the kind of Jewish conversion to Christianity that we have seen throughout church history.
Given this analysis, Grudem concludes that Christ's return is imminent, and that the only the unfulfilled "signs in the heavens" could be used as a predictor. However, because they may last only an extremely brief time, we must admit that Christ could return at any time, and we cannot predict his coming:
The only sign that seems certainly not to have occurred, the darkening of the sun and moon and the falling of the stars, could occur within the space of a few minutes, and therefore it seems appropriate to say that Christ could now return at any hour of the day or night. (Systematic Theology, chapter 54)
Ladd's approach is similar. Dealing with Jesus's predictions in the Olivet Discourse, he writes:
The Olivet Discourse describes no signs by which the end can be calculated. [...] False messiahs will arise; wars will occur; "but the end is not yet" (Mark 13:7). These events are not signs of an imminent end; they will occur, but the end delays. Rather than being signs of the end, they are only "the beginning of woes" (Mark 13:8) which will mark the entire age. (The Presence of the Future, 326–27)
Ladd thus sees "no conflict between the Olivet Discourse and Jesus'saying that the end will come without signs which can be calculated." Other signs that he accepts, like that of the Gospel being preached to all nations, can't be used for calculations either, since it is difficult to know when they are fulfilled.
Post-tribulation premillennialists, and more generally most non-dispensationalists, are hesitant to literally interpret the Bible's apocalyptic passages. Thus, they typically do not see any of the events signalling the return of Christ to be sufficiently specific as to allow anyone to calculate the date of Christ's return.
Thus, Matthew 24:36 and similar passages do not need to be explained: "Post-tribs" hold that Jesus is clearly teaching that no man can know the day or the hour, and neither can any man predict it on the basis of the fulfillment of signs.