Elixirs duration.

Greetings,
Could you fix the issue of the elixirs not being able to extend the duration of the effect after overlap purchasing ?
If this is not possible could you at least make it possible to renew that certain elixir even if it's not expired yet ? Because sometimes it bugs to wait untill that elixir gets expired to buy new one especially when you are using a combination of buffs and you need them to run together for example experience and damage bufffs.

Or can we buy multiple time so we can buy up for few hours maybe because we need go to old town to buy again