Pre-purchased timed tickets

In London or Dublin, are entry times strictly enforced with pre-purchased tickets, such as for the Tower of London, the London Eye or Trinity College in Dublin?

I don't think that The Tower has 'timed' tickets.

The London Eye says: "Ticket holders for London Eye Fast Track tickets (including disabled guests and groups and schools) must arrive at the entrance to the Fast Track line 15 minutes prior to the experience time printed on the ticket. " and "Latecomers will not be admitted to the London Eye except at the absolute discretion of LEMS." How this works in practice I don't know, but I have not heard of anyone being turned away for being late. They also say: "What happens if I'm running late? - We understand that circumstances beyond your control can result in you arriving to the Coca-Cola London Eye later than your arrival time slot. If you are running late, please speak to a member of our team onsite and they will endeavour to ensure your entry at the next available time. This may involve a small wait and may also incur a £10 rebooking fee."

As far as I can tell, Trinity College has a fairly laid-back attitude as you might expect in Dublin. The queues are rarely very long unless you arrive behind a tour bus.

I purchased advance tickets to The Book of Kells last year before Celebrity changed our arrival time into Dublin. I emailed Trinity College and the told me the tickets would be honored. We had no problems although we were late for our ticket reservation.

We had a timed ticket for Trinity College and the time wasnt checked when we walked up to the entrance. The line to the Tower of London can be very long depending on time of day. People that purchased the London Pass have a different entrance, sort of a fast pass type line.

I booked tickets for book of kells in July same day online. It was a last min decision and we ended up an hour early around 1030. There was nobody in the prebook line so they said it fine for us to go in which was great. There was a long line for those either without tickets or waiting for tickets.

It’s best to go to the Tower of London when it opens. There were about a 100 in front of us but once we went through everyone disappeared. Once inside definitely head straight for the Crown Jewels because you’ll notice as you get there the long roped queue lines that are empty but will be full when you come out.