Hi

you need a site workflow that is scheduled to do this. I have an example documented here

Site Workflow - Document Review Date Approaching Reminders‌

for your case you will want to

• calculate date today + 30 days (compare to employee start date)
• calculate date today + 14 days (compare to employee start date)
• calculate date today + 7 days (compare to employee start date)
• employee date <= current date

I still dont know how to do that, I have in form field where someone from HR fills up when will new employee start, that can be for 5days, 10, 20, 30... How can I use that filed from Form in Calculate Date in Workflow?

did you look at the example?

is the start date field in your form also saved in a list column?

I saw your example few days ago, and I tried to build something like that but I had problems, and didnt know how to create it to work... I have Custom List and I have column Start Date, and same field in Nintex Form, where someone from HR type exact date when will new employee start. I would like to remind on tasks depending on that date (if new employee starts in 45days to remind 30days before start / or if its start in 7 days to remind every day). Thank you very much for your time! 

i will try and do exact demo for you soon - are you still struggling with this one?