Solver time

I have the following problem

t3 = time()
Z_OP = Model(with_optimizer(CPLEX.Optimizer))
t4 = time()
if RE ==2
    @variable(Z_OP, 0 <= x[l,m] <= 1 )
    @variable(Z_OP, x[l,m], Bin)
t5 = time()
for i = 1:size(A,1)
    @constraint(Z_OP, (A*x)[i,1] .== 1)           
t6 = time()
@objective(Z_OP, Min, sum(B*x))
t7 = time()

when I run the model, t6-t5 is very large if I compare it with t7-t6.

For 220 constraints and 24310 variables:
t6-t5 = 105.4s
t7-t6 = 0.304s

I have no idea what that time (t6-t5) refers to or why it takes longer in that step. Anybody can help me, please!!!

It is the time to build the constraints. Here, you could speed it up by avoiding to compute A*x many times.
You can compute Ax = A * x just once outside the loop or even do A[i, :] * x[:, 1]