How to check DNS propagation
DNS propagation is the time it takes for a new record value to spread across resolver caches in different networks and countries. While the old value still lives in someone's cache, some visitors reach the site at the new address and others at the old one. What really sets the speed is not a magic 24 to 48 hours, but the TTL of the record you changed. Here is how to check the state of propagation and tell when it is finished.
Check your site
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Find out what you changed and its TTL
Open cPanel > Zone Editor and locate the changed record (A, CNAME, MX, or NS). The TTL value shows how many seconds resolvers will keep the OLD value cached: 3600 is one hour, 14400 is four hours. It is the old TTL, not the new one, that sets the upper limit on waiting.
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Ask the authoritative server directly
The authoritative server (for TomisHost that is ns1/ns2.tomishost.com) always returns the current value with no caching. From a terminal: nslookup -type=A your-domain ns1.tomishost.com (or dig @ns1.tomishost.com your-domain). If the new value is already here, the change was saved correctly and all that is left is waiting for caches to expire.
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Check from several resolvers and locations
Public resolvers update at different times. Compare the answer from 1.1.1.1 and 8.8.8.8 (nslookup your-domain 1.1.1.1) and run the domain through a global DNS checker. If some points show the new value and others the old one, propagation is still in progress, which is normal.
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Flush your own cache so you are not fooled
Your computer and router cache DNS too. On Windows run ipconfig /flushdns, restart the browser, and reboot the router if needed. Otherwise you will keep seeing the old value locally and think propagation is stuck.
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Judge by TTL, and for NS changes by the registry
For ordinary records propagation finishes within the old TTL. For a nameserver (NS) change there is extra caching at the top level domain, so it can realistically take up to 24 to 48 hours. You cannot speed up the current change anymore, but for next time lower the TTL in advance.
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For an NS change, verify the delegation
If you changed nameservers, make sure the domain is delegated to the right NS: check the domain's whois or use the TechGuard whois tool. As long as whois shows the old nameservers, the new zone will not even be read.
How to verify the result
Propagation can be considered done when the authoritative server, the public resolvers (1.1.1.1, 8.8.8.8), and a global checker all return the SAME new value. To gather every answer in one place and see A, CNAME, MX, NS, and TTL at a glance, use the free TechGuard DNS checker.
Tip: The most common mistake is lowering the TTL at the same moment you change the record. That will not speed up the current propagation, because resolvers already cached the old value with the old TTL. Lower the TTL in advance, a few hours before the planned change.