Always best to squeeze your lemons on the spot, prior to drinking.
Live Enzymes in most fresh juices are gone/dead in minutes,though
some inert enzymes to make it through the day, it is always best,
whenever possible ,to drink(any veg/fruit juice) within 2-5 minutes.
here is an example of a great ,natural, environmentally lower impact,
juicer. Great for oranges,too...I like to keep things simple...