De brevitate vitae 9.5

I am having a bit of trouble understanding the syntax of the infinitive pervenisse in the following passage:

Quemadmodum aut sermo aut lectio aut aliqua intentior cogitatio iter facientis decipit et pervenisse ante sentiunt quam adpropinquasse, sic hoc iter vitae adsiduum et citatissimum, quod vigilantes dormientesque eodem gradu facimus, occupatis non apparet nisi in fine.

I think I understand the sense of the passage: It is as if one lost in thought discovers that he has already reached his destination before he even realized that he was drawing near to it. Literally, “…and to have arrived before they sense that they had approached…” The infinitive seemed to be left hanging. The second, I think, is indirect speech after the finite verb sentiunt. Can anyone explain? I would be especially thankful if somebody could refer me to the relevant section in Allen and Greenough a copy of which I have on my shelves.

I think what throws you off is the split* antequam with words inbetween (maybe also the fact that both infinitives rely on the same verb). Maybe this is clearer:

et pervenisse sentiunt antequam adpropinquasse (sentiunt).

https://dcc.dickinson.edu/grammar/latin/antequam-and-priusquam

*“Split” may be the wrong word here since antequam is nothing else than ante quam after all.

Thank you very much, Shenoute. That is exactly what my problem was. The reference to Dickinson was especially helpful.

How silly of me. I just realized that the link to Dickinson is indeed Allen and Greenough. Much apprecieted. I prefer to read in hard copy when I can.