Not all offices will except your application at any time. Bangkok will, others are mostly once you have 15 days remaining but some will tell you to come back in the last 7 days during busy periods.
Have a look at the 12 month Multiple entry O visa available in London for those of 65 and over and drawing a state pension. You simply need evidence of drawing a state pension.
What I will say about these land borders at holiday times, and particularly the Malaysian and Burmese crossings, is they are rammed with people. I don't know about foot traffic times but it's not unusual for it to take 4,5 or even 6 hours to cross with a car into and out of Malaysia. I've done it a number of times. Any weekend can be bad too.