Hi Luby & welcome! Your profile says Washington State, so you definitely did the right thing in taking the Flow super off for winter
If last year was your very first season with a new colony, it makes sense that you didn’t get much of a harvest. That’s the way it goes with almost any beginning colony in a temperate climate. So don’t worry - now that your colony has presumably survived the winter, you achieved a huge goal already! And now the Flow super is all waxed up & ready for your blackberry & apple season!
As for timing of putting the super back on, you need to ensure that your colony is -
Healthy, with the queen laying consistently
Built up to proper wintering capacity
Bustling with bees on all frames
Able to find LOTS of nectar out there
Do you know an experienced local beek who can help you with a more specific supering time?