I can watch ITV hub on my Now TV box ad free for about 1.5 hours but suddenly I get ads in the place where ad-breaks would normally be. I've discovered that if I exit the ITV Hub app then restart & resume the programme I was watching the ads do not reappear. It's as if there's some kind of timeout or ttl somewhere.
It happened fairly late last night so I didn't get a chance to look at the PiHole log, I have 'itv-ads.aimatch.com' in my blacklist.
I don't fully understand this but I was kindly told about CNAME cloaking in another thread (Odd behaviour from log file - #9 by Bucking_Horn), it seems that tom.itv.com cloaks itv-ads.aimatch.com with a TTL of 60 mins so I suppose it's possible that my NowTV box is re requesting tom.itv.com and what I thought was 90 mins, was actually a bit over 60 mins. In any case, I've now blacklisted tom.itv.com and will see what happens.