When is the best time to buy airline tickets ?

Now, sometimes booking on a Tuesday gets the best rates.

Usually, in normal circumstances, you should book now your July air ticket (particularly when it is an international air ticket) because July is part of the summer peak season with expensive airfares.

Read more here:

http://www.willgoto.com/1/147195/liens.aspx

The covid-19 pandemic makes current demand loxwer than usual. However, demand (and prices) will probably peak up later as the pandemic eases. So, booking now may remain adviced.

However, you should book now only if you are sure to be able to travel as expected in July. Anyway, you had better book air tickets that are changeable or refundable or with flexible terms. 

From where to where?  

Now is a good time to start looking at prices, but too early to book in normal times. But travel patterns are so disrupted now that I think it's hard to say what's the best time to buy. It partly depends how important it is to you to have certain dates. If it's really important, buy early. If not, wait a bit longer

I've read that the ideal time is 64 days out.  I travel fairly often, at least I did before Covid.  I would start tracking prices months out, and watching for patterns.  I generally use Expedia, as they've been cool when I had to cancel.  Southwest doesn't use third party sellers, so you have to check on their website directly. 

I'd start checking a couple times a day, sometimes, there's a sudden drop, and if you can snag them then, you can save a bundle. 

It all depends on where you are, where you intend to go, what the travel conditions are, whether lockdown has eased, whether travel depends on being fully inoculated for covid and how popular the destination is.

If you can travel and want to buy a ticket, I personally would do so now in case they are booked up by the time you want to go.  However, if whichever country you are in/intend to travel to is still in lockdown, I wouldn't bother booking until you are certain it can happen - unless you can get insurance to cover a cancelled trip.