You will be able to claim rewards from the app (if you used Maiar) or from the web wallet. Every 24 hours new rewards become available to be claimed. You can claim them when you want. If you don't claim them you don't lose them, they will stay there waiting to be claimed. There is no way to automate the claim of the rewards.
Keep in mind, you can stake the rewards as well so you can compound the rewards and increase the overall rewards received. There is NO minimum of EGLD when you stake/compound the rewards (as opposed to the 1 EGLD minimum when you stake). When staking rewards please consider the fees involved for the transaction itself (less than 0.001 EGLD).
Please see the following image for a calculation made by the community regarding best scenarios around compounding rewards.
The rewards for the first days are smaller; we have to wait until more nodes are activated. By the 10th of April most of the nodes will be active and your subsequent rewards will be higher. Also Elrond is removing 363 nodes in the following days, making room for more nodes to be activated and when this happen the APR will get closer to the current estimated target: 19%. Keep in mind that by staking your rewards and by compounding them your actual final APR can be higher with up to 3%, so close to 22%.