Long before Warsaw had a mosque serving recent immigrants, Lipka Tatar communities were settling in the Grand Duchy of Lithuania — territory that today spans parts of Poland and Belarus — from the 14th century onward, granted land by Grand Duke Vytautas in exchange for military service. Their descendants still maintain the wooden mosques of Bohoniki and Kruszyniany in the Podlasie region near the Belarusian border, among the oldest Muslim houses of worship in Europe outside former Ottoman territory, though the Tatar community itself today numbers only a few thousand.
Warsaw's own Muslim population is a separate, much larger and more recent story, made up mainly of immigrants and their families from Chechnya, the Middle East and North Africa who have settled in the capital since the late 20th century. Warsaw sits at roughly 52°N, giving it long, bright summer evenings and short winter days — a seasonal swing pronounced enough that Fajr and Isha times shift by well over an hour between June and December, quite apart from the roughly 200 kilometers separating the capital from the historic Tatar villages further east.
Poland's small and historically diverse Muslim population has no unified national fatwa council of its own, so mosques in Warsaw and the Tatar communities of Podlasie alike generally follow the Muslim World League's 18°/17° angles, the same standard used across most of Central and Western Europe.
No — Warsaw's mosques serve its modern immigrant community, while Poland's oldest surviving mosques are the centuries-old wooden Tatar mosques of Bohoniki and Kruszyniany, built by Lipka Tatar settlers in the Podlasie region.
No — the Lipka Tatar minority numbers only a few thousand today, while a larger and more recent immigrant Muslim population, concentrated mainly in Warsaw, has grown substantially since the 1990s.
Considerably — Warsaw's roughly 52°N latitude means winter days can run under 8 hours while midsummer days stretch past 16, pulling Fajr noticeably earlier and Isha noticeably later as the seasons turn.
Yes, Poland shifts clocks forward in spring and back in autumn along with the rest of the European Union, which moves every prayer's displayed clock time by an hour on the changeover weekend.