Deca has a longer half life then test e so some people will recommend stopping the deca a few weeks prior to the test e but that's truthfully nit picking and not needed at all.
Test e has a half life of 10.5 days. Deca is 14 days. The difference is so minimal it isn't enough to concern yourself with.
Deca is a liver toxic oral steroid so you only want to use is the first couple of weeks of your cycle.
I recommend 12 weeks for a test/deca cycle.
Remember to include the proper support supplements with your cycle:
1. An AI to keep estrogen in the low-normal range. Aromasin at 10mg EOD is a good dosage.
2. An anti-prolactin drug to keep prolactin in the low-normal range. Cabergoline at 0.25mg EOD is a good dosage.
The support supplements are very important because high estrogen and prolactin levels can lead to side effects like gyno and water retention.
I would also add in a good liver aid supplement like n2guard from n2bm.com when using the dbol because it is a liver toxic oral steroid.
Here's what I recommend:
Weeks 1 - 12
testosterone 400mg/week
deca 250mg/week
aromasin 12.5mg every other day
cabergoline 0.25mg every other day
Weeks 1 - 6
dbol 30mg/day
n2guard 7 capsules/day
After your cycle run the perfect PCT protocol:
http://www.evolutionary.org/the-perfect-post-cycle-therapy-pct/