If there are shoulders on the road before and after the ramp, you may be able to wait for a gap. In this case, you can decide on (i) how comfortable you are in the lane, and (ii) whether motorists or police attach any weight to the obligation of drivers on the ramp to yield to traffic (including you) on the road.

Given a choice, it sounds simpler to me to ride in the straight traffic lane until you are past the merge. Then you can move on to the shoulder if you think it is safe or convenient. If motorists think you are required to use any shoulder (varies by state) or police consider motor vehicles to have the right of way and bicyclists at fault in any collision (depends on officer), you may want to give up the right of way if it is not enforceable.