[Eurytus]

Actually if you read the book “The Middle Earth Atlas” by Karen Wynn Fonstad (I think it is or similar) this problem is looked at in some detail.
Bilbo’s journey to Rivendell actually takes far longer than Frodo’s. So much longer in fact that when you consider it in terms of miles per day it becomes almost ludicrously slow. Even more so when you consider that all the Dwarves and Bilbo were mounted whilst the Hobbits in LOTR usually were not.
Also Bilbo’s journey through the Trollshaws was suspiciously quick as well as the issue with the Troll’s fire being visible from the road whereas in Frodo’s case it appeared to be someway distant.

The only real answer is that the geography was far more fluid in the Hobbit, especially west of the Misty Mountains.