One divine glow recharges about every ten minutes. During this time, play quests and puzzles to keep productive. You will also get mana as as a result and do not cost any divine glow to try.
Reactions
Tap the checklist button at the bottom right to view your combination history. This lets you keep track of which combinations were successfully used to create a new reaction. This helps you to avoid making the same element again. Note that some elements may have multiple reactions that can be used to crate them. If you find an alternate reaction for an element that you have already discovered it will be a waste of divine glow.