I've just been working on an article with Glynn Freeman on 'how to catch more fish', i.e. how to fish more efficiently, which will appear in the July issue of the magazine. One of the things he'll cover is timing of one's fishing effort; I noticed something he mentioned off the cuff at FF&FT's recent Salmon School: when the birds start singing, high pressure is on its way, and salmon feel good and might, just might, take. I wasn't conscious of this before, and hadn't made the connection, but when I thought about it I was sure he was right.

Myself, I'm a great believer in timing my fishing with changes of light, especially when fishing for migratory fish. I've noticed sea trout will take just as darkness falls; at the darkest, blackest part of a summer night; particularly as the first light of dawn breaks in the west; and also as soon as the first shafts of sunlight creep onto the river. If the night is cloudy then the subtle changes from lighter to darker (yes, this can happen even in the middle of the night) can trigger a take.

For salmon, I love to get on the river as the evening light fades towards night; it's a very narrow window. So narrow, that if you are lucky enough to hook one, it is usually too dark to carry on after you've landed it. It's a one-fish window. If I had to describe this time of evening I would say it's a fraction before you start to struggle to see exactly where your fly has landed. Or, I could tell you that for this week that time (where I fish) is precisely 8.50pm.

Monday night was clear, as it had been all day, with a pig of an upstream breeze. I had been wading deep, the temperature was dropping, and I was about to pack in. But what about the top of the pool? What about a last-light throw? Surely this air temperature drop would scupper my chances? In for a penny ... A short drive, and after five minutes of casting I was playing a nine-pounder – my first of the season. Back in my car, I back-calculate the time I hooked it. It was 8.50pm.

Wednesday night, I play out the same routine, it's again clear and cold and no sign of a fish. I'm shivering as I climb out of the pool, but drive up to the pool ... just in case. On the radio, Manchester United are just kicking off in the second half against Schalke in the Champions League semi-final as I clamber out of the car. It's bang on 8.45pm. Minutes later, I'm connected to a fish that I cannot persuade across the river. It's made an explosive run downstream, ripping line powerfully off my reel. Having followed it 30 yards downstream, I lean on it with my 15-footer to persuade it to my side, but it won't budge. I'm worried about the fine-wire hooks I use. Any more of this and they'll open out. So we play tug-of-war for what seems an age. I apply side-strain to get it off balance. No joy. I try pumping the fish to gain line on it, but it refuses to come to my side of the river. The longer I play this fish, the bigger it grows in my mind. Now there's a horrible grating on the line and a worrying solidity. Rocks. How much shredding can 15lb Maxima take? Plenty. Now it's free again. Fingers crossed. At last element of swirls at the surface. I'm winning. Banjo, my spaniel, has waded in, waiting to greet it, but I persuade her out … it might swallow her!

Eventually, when I beach it in the shallows, I realise how deep this fish is. And how silver. No sea lice, but it's only been in the river for a few days. Its flesh is rock-solid, like a tuna. It's male, with a suggestion of a kype on the lower jaw. The fine hook nicks out quickly and I hastily measure its length, tail to nose-tip against my rod as it lies in the shallows. Rod butt to butt-ring whipping. Over three feet. I run the tip of my fly line around its girth - at the front of the dorsal fin and stretch this length against my rod butt. 27 inches. It's like a little silver pig! No camera, no phone. Typical. I ease it back into deeper water and within a minute it swims away powerfully. Next day, I calculate its weight from calculators on the internet. Estimates vary – from 20-40lb(!) – but I decide to put it at 22lb, having seen similar fish before.

I check the time: 9.22 pm. This salmon took at exactly the same place as Monday's fish, at exactly the same time – 8.50 pm. Hmm, guess where I'll be tonight!