A.T. Robertson Commentary Hebrews 4:7

"he again defineth a certain day, To-day, saying in David so long a time afterward (even as hath been said before), To-day if ye shall hear his voice, Harden not your hearts." — Hebrews 4:7 (ASV)

He again defineth a certain day (παλιν τινα οριζε ημεραν). Present active indicative of οριζω, old verb to set a limit (ορος, horizon) as in Ac 17:26; Romans 1:4.

In David (εν Δαυειδ). Attributing the Psalm to David or in the Psalter at any rate.

Hath been before said (προειρητα). Perfect passive indicative referring to the quotation in 3:7,15.

After so long a time (μετα τοσουτον χρονον). The time between Joshua and David.