TAT's website for Songkran is showing the festival taking place on different dates in various locations around the country. Dates for Pattaya's Wanlai/Songkran festival are:
Is that long enough for you?
It seems to me that additional days are added to the traditional 3 day festival every year. Also, in previous years I'm pretty sure Pattaya celebrated Songkran the week after Bangkok in order to attract Bangkokians down to Pattaya for Songkran part 2. This year the dates appear to clash. I guess I'll only really know when I get a bucketful in my face!!!! Roll on May... I know, grump, grump, grump.