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"how long do you usually have to wait until you switch it to a bigger pot?"
You can transplant at anytime but you should transplant no later than when you need to water it too often. For a cup if I have to water it every day it goes to a new pot. We're concerned about root growth at this stage, clear cups will let you watch your mining operation in action.
The seedling in that picture does not need to be repotted. Do you have holes in the bottom of the can? Very important. When you water soak your pot until water drips from the bottom, then elevate the pot so the water drains. These air pruning cups eliminate root rot in seedlings.
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