May the council delay the effective date of a charter amendment for an extended period, for example for two or three years?

Probably, but only for changes that the council has itself initiated. The General Assembly sometimes delays the effective date of charter amendments that it enacts, and this statute is intended to give the council authority that is comparable to the General Assembly's. There may be good reasons for such a delay. For example, the change might be to increase the size of the council in a city that elects its council members to nonstaggered four-year terms, and the next election might be three years away. Although it would be possible to elect the additional member or members for two-year terms in an interim election, the city might prefer to avoid the expense of that otherwise unnecessary election.