Reading timestamp values from Datums gives garbage values

Hey,

I'm trying to read a timestamp column as EPOCH.
My query is as follows.
```
SELECT EXTRACT(EPOCH FROM timestamp_column) FROM table;

column
----------

1716213097.86486
```
When running in the console this query gives valid epoch output which
appears to be of type double.

When trying to read the query response from the Datum, I get garbage values.
I've tried various types and none of them read the correct value.
```

Datum current_timestamp = SPI_getbinval(SPI_tuptable->vals[i],
SPI_tuptable->tupdesc, 5, &isnull);

double current_time = DatumGetFloat8(current_timestamp); // prints 0

int64 time = DatumGetUint64(current_timestamp); // prints 5293917674
```

Can you help me out with the correct way to read EPOCH values from datums?

Thanks,
Sushrut