Allow specification of retrieval time span

[ohookins]

I believe the retrieval cost calculation is based on the 4-5 hour retrieval job time (or at least, a single 24-hour period). In the case of very large data storage size we may want to split up the retrieval across several days to reduce costs.

Therefore it would be nice if the total retrieval time could be specified in the interface.

[fmasi]

This would indeed be a nice feature to have.