Dig down a bit and check one or two of them... see if there is any radish at all below the soil line. If there isn't, they were likely planted too close and not adequately thinned. Radishes won't "radish up" if they aren't thinned early.

If there are no radishes formed at all, waiting won't help. Pull them, eat the greens, and plant your melons. :)

I planted 16 seeds per square. No thinning. All were planted 3" apart which corresponds to the seed packet requirement.

I checked them again tonight. The leaves are still small on a few of them. I poked around a few of the larger ones and didn't find any radishes. I pulled one and saw the red root was less than 2" long and thin.

These are Pink Beauty, an early variety that should mature in less than 30 days. Going to pull them and plant something else. Also going to try and plant them in the ground and see if it makes a difference.

I plant radishes every year and never manage to get decent radishes. I've been told it's because my soil is too nitrogen-rich. Which makes sense, I guess. Compost adds a lot of nitrogen, generally. You could pull up just a few of the radishes and start the cucumber seeds if you want to let the radishes go a little longer. My cucs usually share a box with other early crops until they get big enough to block out the light below.

My experience is that radishes take longer to start forming than might be expected... and then really develop... I suggest giving it more time.

Manda,

I did as you suggested. I pulled some of the radishes to make room for the other plants but kept some around the edges until the other plants come in. When I pulled them I noticed on some the radish looked like it might start developing. A couple days ago I noticed the red pink balls peaking out from the soil. Thanks for the advice.

I had the bed covered with greenhouse plastic over winter and while I was starting seeds. There were a couple of days where I forgot to remove it when it was very hot and I wonder if that was a factor.