Freezing breastmilk into cubes

Any ladies out there does this? I’m exclusively breastfeeding and i only use my haakaa in the morning. I get around 3-4oz every morning and just started separating them into cubes. Since i’m planning to head back to work and baby might be able to have her first meal on her 4th month, i thought cubes would be the easy way to go.

I would take about 2-3 days to completely fill up the tray. Is it bad/unhygienic if i keep taking it out from the freezer to fill up the slots? I’m using a rubber ice tray with lid and i would store 3 days of milk cubes into a bag and dated at the earliest date.