How can I increase the lock screen delay? On my HTC One V (Android 4 Ice Cream Sandwich), I can use "Settings / Security / Lock Phone After" to set the time, after which entering the PIN is required to unlock the screen. The maximum setting here is "15 minutes".

Practically, this means I have to enter the PIN every time I take the phone out of my pocket, too often for my liking. Can I increase this time span to something > 1 hour?

PS: I have encrypted my phone. I understand that I am taking a risk, when someone should steal my unlocked phone.
Try using Delayed Lock - works with ICS but you need to be rooted ONLY if you want Pattern Lock. PIN and password lock do not require a device to be rooted to use this app.

There's a trial version which I highly recommend you try and use before making a decision. There are also available free plugins to automatically keep the device unlocked while connected to a specific WiFi network / Bluetooth device or at certain locations.