In more detail
It can hint at when a sample was built, but it is trivial to forge, and many modern builds set it to zero or a hash for reproducibility. Treat it as a clue to cross-check against other evidence, not as proof. See Unix timestamp and Timestomping. In a Portable Executable (PE) file the value is the 32-bit TimeDateStamp field of the COFF file header, eight bytes after the PE\0\0 signature, stored little-endian as seconds since 1970-01-01 UTC. Debug directories, resources and digital signatures can carry further timestamps worth comparing.
Why it matters
Analysts use the stamp to cluster samples from the same campaign and to place a build in a timeline. A date in the future, before the compiler existed, or out of line with the signing date suggests tampering; with reproducible builds the field may not be a date at all, so a "1970" or odd 2050 value is not by itself suspicious.
Example
In the 64-bit gui-64.exe launcher shipped with Python's setuptools, the PE signature sits at offset 0x100:
00000100: 5045 0000 6486 0600 ea27 6864 ...
P E \0\0 machine sections TimeDateStamp
The bytes EA 27 68 64 read little-endian give 0x646827EA = 1684547562, which is 2023-05-20 01:52:42 UTC. The Executable Forensics decodes this field automatically.