Pokemon-go – way to check how many consecutive days I’ve gotten the Daily Bonus

You are eligible to claim the "Defender Bonus":

• Once every 21 hours
• If you have at least 1 Pokémon in a gym at the time.

One you have claimed your bonus, you will need to wait 21 hours before claiming it again.

You can gain additional bonuses if you have 1 Pokémon in other gyms as well (you can assign 1 Pokémon to multiple gyms, but you can't have multiple Pokémon in the same gym), which will increase your reward. However, this still is only available once every 21 hours, from the time you last collected your "Defender Bonus".

• Adding Pokémon to new gyms does not reset the clock
• Losing a Gym does not reset the clock
• Changing the time on your phone does not reset the clock^{[citation needed]}, as all user information is stored on the servers.

Therefore, the only "strategy" I can suggest is to

1. Maintain your gym, so you can maintain your defender bonus
2. After the countdown ends, add Pokémon to as many gyms as you can, then claim your bonus, before you lose the gym.

This has changed, as of June 22, 2017

The Old Defender bonus was replaced with an automatic reward system, granting a player 1 coin/10 minutes a Pokémon was active in a gym (raids will place a gym "on hold", and Pokémon will not claim coins in this period, or lose health over time); to a maximum of 50 coins per day, that resets at midnight, and is automatically claimed when Pokémon are kicked out a gym.

This means that if you have 1 Pokémon in a gym for 8 hours and 20 minutes (500 minutes) you will gain the max 50 coins. Any other Pokémon that are in gyms in the same 24-hr period that you claimed this reward will no longer reward you with coins.

The way to maximize stardust is to gain as many trainer levels as you possible can first, and then use it on pokemon that are close to maxing out anyway.

If you use it on a low level, it'll be a waste because in a couple of levels you're just going to find pokemon more powerful than the one you upgraded. So gaining as many levels as possible is your first priority.

That logic will always hold -- it is ALWAYS better to save your stardust until you're a higher level. But at some point you'll bite the bullet and decide you want to upgrade some pokemon now and do some battling. In that case, look at the half circle above the pokemon. This is an 'Upgrade Meter', where if it's filled all the way to the right, you can't use any more stardust. Pokemon you catch might start out with any amount of that already filled up. So use your stardust on a pokemon that's already mostly done for you.

See here for an example of the pokemon screen with the upgrade bar: http://imgur.com/r/pokemongo/mYu8Njh

In that case, the pokemon is about half-way powered up. I'd hold out for one that was already about three quarters upgraded.