I want to do the diagnostic test in the OG 12th, but the instructions say I can take all the time I need, that I shouldn't time it, and that I can go back and change my answers. Is that really a good idea? I thought it's better to time everything, and never go back to a question until I finish the section.
As per my experience if you are just starting GMAT preparation, do not keep pacing with time..first try to understand questions, their explanation including wrong answer's explanation etc...and down the line after few weeks once you see you are correctly doing all those questions, then ONLY keep pacing with time and which would be then a 'MUST DO' activity...
Also see other's comments and keep judging yourself about which strategy really fits with you..it's not true that one specific strategy will fit to everyone..
Hope this help.












