Matt, if you're checking your baggage (bike +?) straight through to Delhi, then 85 mins should be OK--just.
Worth checking to see if the flights out of Edinburgh to Istanbul are often/regularly delayed--what's the turnaround time between the arrival of the plane from Istanbul, and its departure from Edinburgh? I mention this because our flights in N America are often delayed because the inbound flight is late, often 'cos of bad weather.
If you have a 21-hr layover in Istanbul, what happens to your bike & other baggage? Does it stay in the baggage area, or do you have to claim it and check it in again? If it's not too much hassle, and if your bike is secure, that might be the easier option. Could you get several hours' sleep in Istanbul airport? Last time I was there, it wasn't v quiet & restful, but maybe there are lounges where you could kip?
Cheers, John