The longest blooming shrub I've grown is Daphne x transatlantica 'Summer Ice', but the delicately white-edged leaves and the small, scented flowers are a much more subtle beauty than the exuberance of a Hydrangea in full bloom. Summer Ice started blooming with the daffodils and continued right past the first few frosts, but I had to be fairly close to appreciate its charms. It was eaten by voles and I haven't found a replacement yet.

One other long-blooming plant (a vine rather than a shrub) is the American native honeysuckle Lonicera sempervirens 'Major Wheeler'. It is covered with tubular red blooms for about 4 weeks in May and June here, but then after the initial first flush, any new growth also puts out blooms, so it has clusters of bloom all summer without pause in my garden, just not as densely as the spring bloom shown below. I don't know if there are hummingbirds in Europe, but they love the flowers.

I don't know whether other selections of Lonicera sempervirens bloom for as long, and I don't know if either of these would behave similarly in zone 7 Slovakia since I don't know anything about your weather or soils. My area has acid well-drained soil and we have 5 months of very cold and snowy weather in the winter but in the summer can get quite humid with daytime temperatures into the 90's F/30's C.

If you come up with other long-blooming shrubs, I would love to hear about them.