Depends,

Does the data get updated on any of the existing rows?

Does the Source table have a key column that you can use to tell if the data is in the new table or not?

If the data does get updated that makes your job a lot tougher. Because it limits what data you can copy ahead of time because if it is updated after you copy it that what do you do?

Have you practiced how long it takes to copy the table?

35 Million Rows Seems like a lot but you might be surprised how long it takes to copy if you make sure your SSIS Package is using Fast load.

Also Practicing may help you answer some other important questions like what to set the initial size of your database. This will prevent frequent autogrow events which would also slow the insert process down slightly.

If the data does not get updated, and it does have a key column. then you certainly can copy "old" rows over ahead of time. and just copy the rest on release night. Again, Try to practice so you don't run into any gotcha's on release night.