I have had winter blooms take up to 2 months to open and set fruit. Just let the tree do what it does. Don't over water too much

The buds on my Meyer lemon take months to blossom indoors, but open so fast out in the sun. My key lime buds grow much faster inside. I hand pollinated all of my blossoms last year and now I don’t bother. I just let the trees be and make sure they’re not too wet or too dry. When they’re actively growing a give a bit more fertilizer.

So, I don’t need to hand pollinate for them to bear fruit if they are indoors for winter?

Generally no. Most citrus will set fruit just fine without intervention by the gardener, even indoors. This is especially true for a young Meyer, which will tend to set more fruit than it can responsibly mature anyway.

My key lime has been covered in flowers since I brought it inside and it keeps setting fruit even though I never pollinate it. There’s no harm in hand pollinating, but it’s probably unnecessary. As PAC says, smaller trees tend to set more fruit than they can handle anyway and end up dropping it or in the case of the Meyer stopping all growth to concentrate on fruit production.