Should I use “modes of operation” for a single block of data?
Even though you are only encrypting one block at a time, think about what would happen if your input data happens to be the same as a previous encryption.  Even though you are encrypting the blocks days or weeks apart, plain encryption (aka ECB mode) would have the same problems as usual.  Counter/CBC/... are designed to avoid that problem.  If you know the input data won't repeat (sequence number, etc. as part of your data) then you won't have the repeating blocks problem of ECB where identical plaintext, when encrypted with the same key, always outputs the same ciphertext.