On the 1099-B when grouping together personal items sold, what would I put for the "Date sold or disposed" when I sold on different dates?

Although you can enter "Various" as the purchase date, there is no option to enter "Various" as the sale date.  

• If you sold a security on multiple dates, then enter each sale separately with its own date.
• However, you can separate the Short-term and Long-term items and choose a date the is appropriate for the short or long-term type of sale.
• We use the dates you bought and sold the items to figure out your holding period (how long you owned them). 
• There are different tax rates for a short-term period (one year or less) and a long-term period (more than one year).