When should I start work experience? (Year 11)

I’m a Year 11 student, obviously aspiring to be a veterinarian.
As I’m studying for my GCSEs, I don’t know if it’s a good idea to start any sort of work experience. My predicted grades are currently average and although I’m sure I can get minimum 7s in the real thing, it’ll take a lot of hard work and I might just cripple from the pressure. Either work experience will be a breath of fresh air for me or another thing on my plate.
I really want to apply to a Pre-Vet Summer School and this requires excellent grades and lots of animal experience. Although I’ve cared for (stray) cats and their litters and missed days of school just to treat and tend to my sickly cockatiel, I don’t think that this is enough.
I know that it’s really difficult to get a placement at practices but I haven’t tried yet because right now, I think that’s too much for me. It might be best for when I’m in Year 12. So, I‘d like to do volunteering on a farm soon, so that I could also get some lambing experience. I have found a farm but I don’t know when I should start or apply or what to say when I apply. I know that lambing season is peak in the Spring but I don’t know if it’s a clever thing to do when I’ll be possibly stressed out with GCSEs being at its peak. I mean, I could try now but it’s also winter - dark and freezing cold.
What do you think?

I’m a Year 11 student, obviously aspiring to be a veterinarian.
As I’m studying for my GCSEs, I don’t know if it’s a good idea to start any sort of work experience. My predicted grades are currently average and although I’m sure I can get minimum 7s in the real thing, it’ll take a lot of hard work and I might just cripple from the pressure. Either work experience will be a breath of fresh air for me or another thing on my plate.
I really want to apply to a Pre-Vet Summer School and this requires excellent grades and lots of animal experience. Although I’ve cared for (stray) cats and their litters and missed days of school just to treat and tend to my sickly cockatiel, I don’t think that this is enough.
I know that it’s really difficult to get a placement at practices but I haven’t tried yet because right now, I think that’s too much for me. It might be best for when I’m in Year 12. So, I‘d like to do volunteering on a farm soon, so that I could also get some lambing experience. I have found a farm but I don’t know when I should start or apply or what to say when I apply. I know that lambing season is peak in the Spring but I don’t know if it’s a clever thing to do when I’ll be possibly stressed out with GCSEs being at its peak. I mean, I could try now but it’s also winter - dark and freezing cold.
What do you think?