Are there any exceptions to this timeline for specific States, and if so, which States are they?
Yes, there are exceptions to this timeline for specific States. The States with exceptions are Himachal Pradesh, Manipur, Meghalaya and Tripura, as mentioned in the text: "Provided that in relation to the 2[Legislatures of the States of Himachal Pradesh, Manipur, Meghalaya and Tripura] this clause shall have effect as if for the words “fifteen years” occurring therein, the words “twenty-five years” were substituted:".