Add option to read start time from the run_info file

[DaveCasson]

Currently run time for all data download scripts is set by the actual system time, and not the run_info seetings.

This should be updated with a common function to either:

1. Use the utc time if no run_info is provided
2. Use the T0 or start time if run_info provided.

Consideration for forecast vs historic (start and end time) should be considered.