When I know exactly what my itinerary is, I usually go to places like expedia.com, hotels.com, roomex.com, etc well ahead of time and reserve my rooms. I show up at the hotel and everything's good to go.

This time, I'm going to be heading over to Europe and meet up with a few friends and travel to a few cities. We don't know exactly what our plans are. The bottom line is... is there like a minimum amount of time that needs to transpire between the time you make the online reservation and when you can check in? I'm always going to have my laptop with internet access, so my plan is travel to cities/towns and when we find a hotel we like, whip out the laptop, make the reservation, then walk in the hotel and show them my confirmation. Of course, doing this reduces the chances of finding vacancy at our choice hotel since it's last minute, but willing to take that risk, we can always find other hotels. Is this feasible? Thanks.