I've been getting my water temp to 67C, usually up to 69C then adding grain in to get 67C, and maintaining this for 60mins prior to boiling. So far this has been my standard MO for all brews. Reading further though, I realise that higher or lower temps will possibly give dryer or sweeter wort. Wanting to try a mash temp at 62C to achieve a dryer finish on my next Stout should I extend the time beyond the 60min mark to say 90min?

Muggy

Mashing at a lower temperature - 64°- 65°C will take longer but will convert more starches to easily fermentable sugars resulting in a lighter bodied, drier beer.

62°C would definitely benefit from a longer mash - I wouldn't do anything less than 90 minutes at that temperature = 120 might be better.

Muggy,
The balancing act of mash temperatures to get the mixture of enzyme results that the yeast then converts to beer is the challenge. Lower the mash temperature enough and at some point you will get a dry dark beer that is no longer a stout. Part of what makes a stout a stout is mouthfeel, or body. By mashing at lower temperatures, you might move into the range where beta amylase runs along at a decent rate, yet alpha amylase is barely working. You will then get lots of (smaller) sugars that your yeast can turn into alcohol and yield a dry beer (more alcohol). With less alpha amylase products (longer sugars) from the low mash temperature, the resulting beer will have less body.
You could make a great beer, but it might not fit the style characteristics of what you intended. That's one aspect that makes brewing so interesting - good ingredients handled differently make different beers.

Here is the link where I found the table below http://howtobrew.com/book/section-3/how ... ng-defined It is from a reputable source, but I have read that alpha and beta amylase temperature activities overlap more than this one shows.

Thanks guys.
I've got a SMASH of Maris Otter and Nelson Sauvin which turned out very nice last attempt but I thought not quite right. The mash temp for it was around 66-67C for 60mins.
Today I thought I'd tweak it to give a slightly drier finish, but also added 100g of CaraAroma and subbed in some left over Mosaic, saving most of the Nelson for a bigger dry hop.
I'll not push my luck by going too low on the mash temp, keep it at 64C, but span out to 100 minutes.

Other people seems to have problems with their urns and the concealed elements caking up. I've never had this happen and it's always nice and clean, but I realise now after someone pointed it out on another forum that it might be because I don't step my mashes. I get up to striking temp, adjust once the grain is in, and leave it there covered with a sleeping bag. My element isn't kicking in and out, or coming on to raise temp for a step.

For a 100 minute mash I think I'll be doing a temp check at the 75min mark just to be sure.

To ensure the best mash we recommend 90min mashes and stirring on occasion. The stirring helps wash the sugars from the grains.