The problem is, there is no definitive right answer, which is why I don't think you should put a time frame on it as you will end up disappointed if it doesn't come about.
The fundamental criteria the DClinPsy courses use to determine who gets a place is, 'whether you're ready to train as a Clinical Psychologist'. If that sounds nice and wishy washy, that's because it is. Lancaster don't read your application form and administer a general ability test and shortlist for interviews off that, Newcastle shortlist through a strict academic criteria, Sheffield cover academic, clinical and references in their shortlisting. Some courses like you to be very reflective, some academic. This makes it difficult to recommend any single route.
The key skill you learn as you gain experience is reflection - to look at what you did, why you did it, what the outcomes were and to consider what it all means, what worked and what you might do differently. So more clinical experience provides you with more to draw on when applying/interviewing.
There are trainee's who applied and got onto the course straight from undergraduate, some do an MSc, PhD and then get on, some work for IAPT, most work as Assistant Psychologist or research assistants - of these, some do one year and others 6 or more. Other people have worked as support workers, drugs and alcohol workers or in homeless shelters. Some trainees have never met a 'service user' before while others have delivered various types of therapy.
What each person does have in common is that they can show that what they have learned, wherever that was, has helped them grow as a reflective practitioner and that they can apply that to the clinical and research settings they will encounter as a trainee.
Check these out:
http://www.clinpsy.org.uk/forum/viewtopic.php?f=32&t=8733http://www.clinpsy.org.uk/forum/viewtopic.php?f=32&t=145http://www.clinpsy.org.uk/forum/viewtopic.php?f=32&t=8809Also google the BPS website for the 'alternative handbook' - it should be available for free. That breaks down which trainees are on each course.
The ClinPsy forum is the hangout for Psychology. This thread
http://www.clinpsy.org.uk/forum/viewtopic.php?f=32&t=19316 is where everyone tracks their current progress on applying.