You can find an "exit-poll" (realiter conducted telephonically [n=~1.200] on April 19-22) at www.sora.at
Remarkable is, that among those below 30 years (n=133) SORA distributes 28% to SPÖ (probably many exGREENies), whereas among the pensionists (totally n=274) SPÖ would have received only their average of 20% (ÖVP 50%), what would be very unusual in Austria.
Unsurprisingly ÖVP and FPÖ have endorsed indirectly the incumbent, Mrs.OppitzPlörer (FI), what makes her the clear favourite (my guess: 55%). But she has led a coalition of FI+SPÖ+GREENS (later joined by ÖVP), so it cannot be ruled out, that enough FPÖ-voters stay at home for enabling Austria's first GREEN-mayor (Mr.Willi).
The city won't present partial results, the total one will be announced at ~19.00/30 MET.