I have a similar need, I produce a 7 minute replay for horse competitions, it runs for up to 12 hours at a time with a perfect 7 minute delay or any delay of your choosing although it is a 2 system setup. I feed the delay usually right from a single camera but you could also feed it from a vmix output if you need a multi cam setup or the pip with the clock showing. I use a Magnavox DVD model MDR533 I believe. I feed a composite video in and composite or HDMI out . Sounds kinda crazy as I have prob $100,000 worth of gear and you can get this thing in the US from Walmart for about $225 but it is bulletproof. I use it between 50 to 100 hours per month. there are other models as well, they just have larger hard drives but mine has a 500gb drive.