To add to what Yoshi212 wrote, understand that you are travelling on two separate tickets so you don't have a connection. Whilst you've left sufficient time in my opinion, if for whatever reason you don't present yourself on time for the QR flight departure (DL flight hugely delayed, cancelled, etc), the ticket and all segments will auto-cancel. Neither QR nor DL has any obligation to do anything further and you'll likely have to buy a new return ticket to MLE if you still want to travel. These are the risks of travelling on separate tickets, and why some people choose to arrive the day before.