Hi George,
The TXT record is also need to set the TTL. Generally, we also recommend set the TTL of TXT record to 3600 seconds or 1 hour, which will effect DNS propagation time through all DNS system. If the TTL is used more than 1 hour, it may take more times for DNS changes to take effect. However, it can take up to 72 hours for a changed record to propagate any assistance.
Thanks,
Anna Shi