I did this but what should I do
You see I'm quite new at this stuff

thank You!
hope I did everything right and there will be no delay any more

Yes you can insert a known address/domain/subnet into the mysql database:

Ex for subnet:
INSERT INTO whitelist (_whitelist,_description) VALUES ('209.85.%.%','# Gmail servers (common pool, no retry)');

Ex for email address:
INSERT INTO whitelist_sender (_whitelist,_description) VALUES ('sender@domain.com','# My old friend - this is just a comment');

Same applies for anything

The tables for policyd are these:

+------------------------+
| Tables_in_policyd      |
+------------------------+
| blacklist              |
| blacklist_dnsname      |
| blacklist_helo         |
| blacklist_sender       |
| helo                   |
| policy                 |
| policy_training        |
| rcpt_acl               |
| spamtrap               |
| throttle               |
| throttle_from_instance |
| throttle_rcpt          |
| triplet                |
| whitelist              |
| whitelist_dnsname      |
| whitelist_sender       |
+------------------------+

As for the question how long it will take for the greylist:

Well the greylist is by default set to 4 minutes. So basically if the senders mail server retries during those 4 minutes he will still get a retry
After those 4 minutes when the server will retry it will pass.

Basically it depends on the sending server, how soon it was set to retry, most have like 10-15 minutes, but some have way longer times.

For some servers i recommend either to whitelist the domain (like google which has xxxxxx subnets) since when the sender retries it will use a different ip address and it might take longer. Or whitelist the sender address.

Best of luck

After inserting records in tables, must I restart postfix and must I enable greylisting in /etc/postfix-policyd.conf? By default I have greylisting=0. And what else I must enable in configs? I`m sorry for my question, I have not experience enough.