Yes this is the number of days your CRL is valid.
one can create a new CRL before the old one expires, so that they overlap for a short time period, e.g., one day before the current CRL expires. But this is not a must.
The recommended validity period of CRLs depends on your use case and your revocation concept.
One issue of CRLs is that a certificate revocation only comes into effect when the new updated CRL gets published and the old CRL is no more valid.
E.g., yesterday you published a CRL with 30 day validity period. Today you have to revoke a certifciate. But the certificate will be accepted by the client until the nex CRL is published and the current expires (in 28 days).
Therefore , the validity period of CRLs is usually shorter. Something between 1-7 days. But as mentioned, depends on your use case and revocation concept.