Block XP Ideas: Delay Timer

[SomewhatDamaged]

Describe the solution you'd like
A time-based lockout instead of player-based.

Config would look something like:

        #If non-zero, number of minutes until a placed block will give XP for breaking it
        block_xp_delay = 0

        #if block_xp_delay is used, what amount of the original XP should be given
        block_xp_multiplier = 1.0

        #if block_xp_delay is used, should the XP return:
        # 0 as soon as the delay is reached
        # 1 linearly
        # 2 exponentially
        block_xp_multiplier = 0

Why is this feature needed
Ideas for extra ways of handling block XP anti-cheese

Describe alternatives you've considered
Sleeping. Sleeping is always a good alternative.

[SomewhatDamaged]

Updated to add the ability to allow for instant return of full XP, linear return, or exponential return. (As requested in #534)