That sounds like a good first sessiom however I would stop putting treats on their heads for now. Usually apple juice or something is great for encouraging one to groom the other (if it’s usually one sided grooming) or for both to groom each other but it’s best to wait til they’ve built up some trust first.
Ollie may have felt a little stressed but that’s one of the reasons you start off with short sessions
Generally what you do is continue doing sessions in neutral area and increase the time til they can spend hours together with no issues. Then you can progress onto semi neutral. Sometimes when you move from neutral to semi neutral, they can take a bit of a step back but that’s quite normal. Once you’ve built up time in semi neutral, you can then move them to where their shared territory will be and you need to supervise them for 24 to 48 hours. This is known as ‘cementing the bond’
As you said they have their room, I assume that’s where their pens are currently located? So when you get to the final stage (putting them in their final, shared accommodation) you’ll need to deep clean the room so it’s somewhat new to them both 