Can my boyfriend use the visa exemption for multiple entries into Thailand based on his work schedule?

The visa exemption allows Estonians to enter Thailand and stay for 30 days, and from October 1 to March 31, 2023, this is extended to 45 days. Since your boyfriend works on a rotational schedule and does not enter Thailand every month, he should be able to use the visa exemption for his stays in October and December without issues. Further entries in February and April next year should also be permissible under the same exemption.