The picture you have shared is showing a splint and not a cast.
5th meta-tarsal fracture takes 4-6 weeks to heal provided you don't have any other co-morbidities like osteoporosis , vit D3 deficiency and addictions like tobacco use , smoking , alcoholism.
Once fracture has healed , it should not pain while you walk.
Next Steps
consult someone and let doctor examine you after removing splint for pain and then proceed accordingly.