Nine months is a tough age and is also very young. I'll be honest with you, I do not see a lot of spaniel types off lead around here and I have seen them in the field and they are not exactly great at checking in and staying with their owners! They remind me a bit of hounds. So, I'd suggest continuing with the training and not expecting to let him off lead on your hikes for awhile, maybe even a year or so. When he's ready, he'll be ready. You can't really put a timeline on it.
I worked my dogs as little puppies and always have an older trained dog for them to pal around with. I also trained them to check in and I carry food with me when we hike. I don't hike where it's very crowded or dangerous (like cliffs). If they started to not come back to me upon first call -- even if a deer was present, I'd put them back on a leash and go back to basics. I won't let a dog off leash that I can't count on. No dog is perfect, but mine are about 99%. Sam could not be off leash anywhere that had a lot of people until he was a little older (like the beach) but Linus was always really good.
Sam was my toughest with the LLW. He'd lose his mind and lunge. I did dog parks, puppy socials and doggie daycare with him, which actually just increased his other dog obsession and created frustration since he was used to visiting other dogs when he wanted. I used a halti on him for maybe six months, which helped a lot, and I never let him "say hi" on leash. He was pretty slow to mature mentally, too. But, he was great at LLW by the time he was about two years old. Linus was LLW trained at six months. I worked with him harder, was a better trainer, no dog parks or doggie daycare nor has he ever been super interested in other dogs. They are all different!