Sorry no you can not enter them during the year. You will get all the 1099-INT, 1099-DIV and 1099-B for sales for the end of the year by late February. You should be able to import them. But you will need to check each sale to make sure the cost basis imported right.
How to import your 1099
https://ttlc.intuit.com/community/entering-importing/help/how-do-i-import-my-1099/00/26254
If you can't import you can enter a summary of the totals. Then mail the backup statement. How to enter the summary
https://ttlc.intuit.com/community/entering-importing/help/how-do-i-enter-a-large-number-of-stock-tra...
