They should take a couple weeks, but the soil was likely too chilly for them back in April (they are tropicals!), slowing them down.
The problem with planting them so early is that while they are sitting there waiting for warm weather, if they get too much rain/water, they can rot out.
I'd dig one up to see what is happening. If they are mushy, probably they are goners. If they are starting to sprout, you can just bury it back.