The utility gr_read_file_metadata uses parse_file_metadata.parse_header() from gr-blocks to parse and print headers in a metadata file. Currently, the rx_time field is printed with us precision. However, the rx_time is stored as the integer seconds of the UNIX timestamp in an uint64_t plus a double storing the fraction of a second, so the rx_time has more precision. A precision on the order of 1ns is necessary for many ranging applications, since 1us is approximately 300m of range. This modifies parse_file_metadata.parse_header() to print rx_time with 16 decimal places, without losing precision. Aditionally, it adds "rx_time_secs" and "rx_time_fracs" fields to the dict() return value of parse_header(), in case they are ever needed. The "rx_time" field in this dict() is a double, and as such it is unable to store a UNIX timestamp with 1ns precision.