It has been pointed out to me that Michael Patton recently had an interesting blog post about the possibility of Esau repenting in Heb 12:17. It can (and should first) be read here. He cites a number of different English translations. I will only quote two of them here to give different perspectives:
NJB: As you know, when he wanted to obtain the blessing afterward, he was rejected and, though he pleaded for it with tears, he could find no way of reversing the decision.
RSV: For you know that afterward, when he desired to inherit the blessing, he was rejected, for he found no chance to repent, though he sought it with tears.
Let us look at the Greek text:
ἴστε γὰρ ὅτι καὶ μετέπειτα θέλων κληρονομῆσαι τὴν εὐλογίαν ἀπεδοκιμάσθη, μετανοίας γὰρ τόπον οὐχ εὗρεν καίπερ μετὰ δακρύων ἐκζητήσας αὐτήν.
A very literal translation could be:
After all, you-all know that he indeed afterwards, while wishing to be given the blessing (of the firstborn), was rejected, for he did not find room for a change of mind, although with tears he desperately sought it.
Traditionally, metanoia has been translated as “repentance” without much consideration for the context. But the word itself basically refers to a change of mind. The RSV and related translations interpret the text to mean that it was Esau who found no room for repentance. This can lead to the general theological interpretation that there is a time when repentance can no longer be followed by forgiveness. The blog author rejects this option and his solution is to take the final feminine pronoun αὐτήν (it) to refer all the way back to the feminine τὴν εὐλογίαν (the blessing) rather than to the closer feminine word μετάνοια (change of mind).
For grammatical reasons my preference is to accept that the pronoun it does refer back to μετάνοια. However, it is clear that Esau has regretted that he sold his birthright and he was seeking with tears to make his father change his mind. Therefore, I think the NJB suggestion that the change of mind is not referring to Esau, but to Isaac makes better sense in the context. It was too late for Isaac to undo and withdraw the blessing he had already given to Jacob and the result was that Esau could not get the blessing he sought after with tears. With this interpretation it is possible to keep the reference of it to the change-of-mind, and at the same time clarify that it was the blessing rather his own repentance that Esau sought and could not be given.
How people interpret this illustration in a broader theological context can vary. Is there a time or a situation where it is too late to repent? I doubt that this text alone gives a clear answer to that question. In my view the crucial point is the willingness of the person to repent rather than God’s willingness to forgive. I believe the second part is constantly available, but the first part may not be present.