Validity and stay duration are different numbers, and confusing them ruins trips.
Turkey's e-visa is valid 180 days from issue. That is the window to enter. Once you enter, Americans can stay up to 90 days within that 180-day period. Valid 180 days does not mean stay 180 days.
Vietnam's e-visa allows stays up to 90 days, single or multiple entry depending on the $25 or $50 version you bought.
India's 30-day e-tourist visa is valid for 30 days from your first arrival, not from the approval date. The 1-year version is valid 365 days from the grant date, but US visitors are capped at 180 days in India per calendar year. Sources: U.S. State Department, Indian Visa Online Read both numbers before booking flights. The most expensive visa mistake is a return flight dated after your permitted stay expires.
Visa validity is the window you can travel; stay duration is how long each visit lasts. They are different numbers.