You can use those at the start of sentences! Just make sure to follow each of them up with a comma (,) then proceed with the rest of the sentence! At times, it’s important to remember that English is a subject-based language. This means we’d typically like to see the subject at the START of the sentence. However, there’s nothing wrong with starting the way you asked :) If there’s anything else let me know!

Hello Alina, my name is John, nice to meet you. As far as your question goes, yes you can use both terms at the beginning of a sentence. These two terms are used to show frequency and routine. For example: "Once a week me and my children go to the park and fly kites." "In the morning I usually eat breakfast before I go to work." Because neither of the two phrases are clauses by themselves or transitional phrases there is no need for a comma after either of them. Hope this helps.

These particular time references should go at the end. If the time reference is not the main focus of the sentence it should be the last.