NMW and starting work early/working through lunch

Hello A few months ago I received a message from HMRC saying that I should 'check my pay' online because I could be paid less than nmw. I receive NMW and my contracted hours are 9-5 however we are expected to come in and 'set up' 15 minutes before the start of the day. It is a dental practice. We are all over the age of 23. We are only paid from 9 am (once the first patient comes in). I am a trainee but I receive no funding and am considered an employee with an hourly rate of nmw. I have contacted my school (who I did the course with and paid privately for) and they said that it is normal that some practices ask nurses to come in early to set up without compensation. We also have meetings that are scheduled in during our lunch hour and even if the employer leaves 20 minutes for us to have lunch(unpaid), should the meeting time be paid for? My employer said that HR has advised them that the meetings do not have to be paid for, even if they are compulsory. Now I am confused about the advice I read on HMRC page which gives an example of a NMW worker who works in a shop and has to come in early to set up - it says that that time has to be paid for. Could you please advise what would be correct in this instance. Thank you

Hi eg5732,
Please note, HMRC cannot comment on specific arrangements without undertaking a full National Minimum Wage investigation.
HMRC can only provide general advice and signpost to guidance. 
Any time that a worker is required to be at or near the place of work this time is considered to be working time for minimum wage purposes. Additional working time added onto a worker’s shift can be before their shift starts or after it has ended; each of these count as ‘working time’ for minimum wage purposes.
All ‘working time’ should be paid for at minimum wage rates.
Team meetings where attendance is required is working time for minimum wage purposes.
If a worker has to attend outside of their normal paid hours, then this would be counted as working time.  
Workers have the right to one uninterrupted 20 minute rest break during their working day, if they work more than 6 hours a day.
This could be a tea or lunch break.
The break does not have to be paid - it depends on their employment contract.                                                                                                                                                                                                                                                                                                      
Further guidance on the hours of work that count for minimum wage purposes, please refer to:
Working hours for which the minimum wage must be paid
If you are concerned that you are not being paid what you are entitled to, you can contact the Advisory, Conciliation and Arbitration Service (Acas) on 0300 123 1100 or you can raise a complaint to HMRC using the following online form:
National Minimum Wage enquiries and complaints
Thank you.