Cannot be anytime. 
Next parliament on 11 April (see my post above), that means the
earliest polling day will be 30 April.
30 April: Unlikely due to long weekend (Labour Day), many going
oversea for holidays
07 May: Unlikely due to ASEAN summit in Jakarta
14 May: Very likely
21 May: Likely but campaign period will clash with Vesak Day on
17 May, they may want to separate reglious festival from
election
28 May: Unlikely, 1st day of June school holiday, parents
bringing their children oversea for holidays
Will not be in June and after.
21 May: maybe they come out with goodies on Vesak day to woo the
Buddhists...
money will fall form the sky that day.