Applying to medicine

Universities aren't looking for a specific amount of work experience, but instead will expect you to be able to draw on experience to answer questions at interview. What really is important about work experience is how you reflect on it and learn from it.
A hospital placement is brilliant for understanding the role and the challenges of a doctor. You may want to look into volunteering as I found it gave some really useful experiences to talk about at interview. Examples of this could be care homes, St John Ambulance or youth groups, which will all give you you something to talk about when talked about skills such as teamwork, empathy etc.

It depends because there are some that ask for at least two weeks of work experience, like Manchester and Birmingham, I'm not sure about others. However, your point about drawing from these experiences still stands.

I would on the whole say that 2 weeks is the amount of work experience you should be doing, just out of competition with other candidates. (Of course, I'm sure there are plenty of people who will lie, but that's besides the point) 2 weeks, of WE, I think in 1-2 specialties would be good work experience, in terms of just pure CV fodder. In terms of what you actually learn is what I reckon is more important, as said by @damnitsnyge. Quality of work experience matters, and if you're doing some paid work experience online I can gaurantee you you're not learning about what it's like to work in medicine, more just what med schools want to think you know (which defeats the point of work experience). Make sure that you're applying to real hospitals, shadowing real doctors and actually interacting with HCPs (and patients if you're allowed to/ if that's possible), and reflecting as much as possible. This, unless prepared very well, will show during interview and interviewers appreciate a candidate who knows what they're talking about and can draw on personal experience and unique cases that they've seen (maintaining confidentiality of course). A week of good hospital experience should involve the above, and will massively outdo some rich kid who's paid 10k to do "summer camps in medicine".