Defining piece-wise constant hazard function in simsurv package

Question

I am attempting to simulate survival data with a delayed treatment effect. The simsurv package has been very helpful: https://cran.r-project.org/web/packages/simsurv/vignettes/simsurv_usage.html

My approach is to define a piece-wise constant hazard function that has this form:

h(t) = λ1, for 0 ≤ t < T1

h(t) = λ2, for T1 ≤ t < T2

For some reason, the simulated survival curves have large 'steps' in the second interval. My guess is, that I can't use if-statements when defining the hazard function.

If anyone has suggestions how to fix this or knows a scource for explanations on how to define such a formula in R please let me know.

library(simsurv)
library(survival)

# user-defined hazard function with two intervals
piecewise_hazard <- function(t, x, betas) {
  ### calculate hazard at time t
  ifelse(test = (t <= 5), 
         yes = betas[["beta1"]], 
         no = betas[["beta2"]] * x[["treatment"]])
}

### Set simulation parameters
set.seed(1234)
n <- 1000
t_max = 10
# Covariate data
covs <- data.frame(id = 1:n,
                   treatment = rep(c(1,2), each = (n/2)))

# Population (fixed effect) parameters
betas <- c(0.02, 0.1)
names(betas) <- c("beta1", "beta2")

### Simulation
sim_times <- simsurv(hazard = piecewise_hazard, 
                       x = covs, 
                       betas = betas, 
                       maxt = t_max)
sim_data <- merge(sim_times, covs)

fit_km <- survfit(Surv(eventtime, status) ~ treatment, data = sim_data)
plot(fit_km,     #clearly needs to match prior model output
     conf.int = FALSE, 
     col = c("red", "blue"), 
     main = "Simulated delayed effect", xlab = "t", ylab = "S(t)")

# Censoring happens only at the end of follow-up at t_max
fit_km$n.censor[fit_km$n.censor > 0]```