How to actually improve at this
The common mistake is to jump to the hardest tier and grind. It does not work well, because a board you cannot read teaches you nothing except that you cannot read it. The faster route is to sit one tier below your ceiling and play enough boards that the standard deductions stop being things you look for and start being things you see.
When an easy board takes you under two minutes without you consciously hunting for anything, move up. That is the signal - speed on the tier below, not frustration on the tier above.
What the four tiers actually change
Not the rules, and not really the grid size. What changes is the depth of chain the board requires before anything is forced. An easy board will hand you a region with one open cell in it. An expert board will require you to combine a region-to-line lock with a squeeze two rows away before a single cell resolves.
That is why the tier is decided by the hardest deduction a board genuinely needs, rather than by how big it looks. An 11×11 that falls to simple counting is an easy board with a lot of cells in it, and it is graded accordingly.
No repeats, and nothing to wait for
Your device remembers the last few hundred boards it has served you, so a long session will not circle back on itself, and neither will several sessions across a week. Change tier whenever you want; that just draws from a different part of the pool.
Every board appears the instant you ask for it. There is no loading spinner while something is worked out, because all of the checking happened long before you arrived.
It cannot touch your streak
Unlimited solves are recorded separately: a solved count and an average time per difficulty, kept apart from your Daily record. Playing forty boards on a Sunday will not advance your streak, and losing interest halfway through one will not break it.
That separation is deliberate. The Daily is meant to be a small fixed thing you can keep up indefinitely. This is the practice ground next to it, and practice should never carry a penalty.
Common questions
Is there a limit on how many I can play?
No. There is no daily cap and no account to hit a limit on. Difficulty is yours to choose and can be changed at any point.
Will I be given the same board twice?
Not within the last few hundred boards. Your device keeps a record of what it has served you, and it carries across sessions rather than resetting each visit.
Do these solves affect my daily streak?
No, in either direction. Unlimited solves keep their own count and average times, and a streak can only be advanced by the Daily.